differential leveling to cgps stations

III.B. DIFFERENTIAL LEVELING TO CGPS STATIONS

Introduction

A project was undertaken by the California Spatial Reference Center (CSRC) to establish a North American Vertical Datum of 1988 (NAVD88) differential elevation on a selection of continuous GPS (CGPS) stations that are part of the Southern California Integrated GPS Network (SCIGN) array. (Further work is currently being done in other areas of the State but this section will concentrate on the first leveling project completed, which was in Southern California.) The purpose of this project was to establish an orthometric height on the base of the preamplifier of the antenna (BPA) and the geodetic reference mark (GRM) at each selected station which would then be used as vertical control in an adjustment to establish GPS derived orthometric heights (± 2cm) on all the CGPS stations in Southern California (the 10 southernmost counties). This process is to help fulfill the CSRC’s function of providing vertical spatial reference to surveyors and other geodetic users in the State of California. This section will detail the differential leveling process used to establish these elevations.

The CSRC was formed to provide a better source of geodetic, spatial reference to surveyors, engineers and other users in the State of California (CSRC, 2002). The CSRC helps users take full advantage of the SCIGN network (Hudnut, et al, 2001) of over 250 CGPS stations in Southern California. These stations have been rapidly adopted for use by surveyors and other users for the horizontal control of projects. Since the geodetic positions of these CGPS stations are calculated daily and immediately updated after a seismic event by SCIGN/SOPAC, the user community has a free, highly accurate and well maintained spatial reference system in a state plagued by crustal motion, seismicity and subsidence. Utilities available to CSRC users (e.g. SECTOR (CSRC, 2004); HTDP (Snay, 2003; 1999)) allow them to take into account the updated positions yet continue to work in a past epoch if necessary for their particular project.

The vertical spatial component has not been as easy to maintain. Although Southern California has hundreds of miles of differentially leveled first order NAVD88 benchmarks, there is no easy way to maintain or otherwise update the elevations after a seismic event. The immense cost of leveling these benchmarks can no longer be funded by the National Geodetic Survey (NGS), the Metropolitan Water District (MWD) and the local counties and agencies that were largely responsible for the initial leveling networks. The CSRC realized a need to establish orthometric heights on the CGPS stations to provide a maintainable vertical spatial reference for the geodetic users in California. The first step in this process was to establish a differential elevation on a group of CGPS stations that would then be the vertical control for the orthometric height adjustment (Zilkoski et al, 1997; Zilkoski et al, 2003). This section will detail the methods we utilized to establish these elevations on the BPA and GRM at the CGPS stations.

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Preliminary Project Planning (before issuance of contract)

Selection of CGPS Stations

This project was to cover the ten southern counties of California – from the 36th parallel down (San Luis Obispo, Kern, San Bernardino, Santa Barbara, Ventura, Los Angeles, Orange, Riverside, San Diego and Imperial Counties). The first step of this project was to select a group of stations that would provide a good geometry over these counties in the final adjustment. With a finite budget in mind, we had to determine the number of stations to level to, the specification to use, the equipment to use, the proximity of the station to existing NAVD88 first order benchmarks, the vertical stability of the station (proximity to seismic or subsidence areas, etc.) and the type of CGPS monument.

The CSRC works in conjunction with the NGS and it was important that upon completion these elevations would be accepted into the national database, so we decided to complete the leveling at the Second Order, Class II criteria of the FGCS Specification and Procedures for Electronic Digital/Bar Code Leveling Systems (FGCS, 1994). This specification would be accepted by NGS and would also provide an elevation ≤ 5mm accuracy. This accuracy for our vertical control would allow the CSRC to achieve the end goal of orthometric heights at ± 2cm accuracy as stated in the CSRC Master Plan for the Geodetic Control (CSRC, 2003).

One mandate of the CSRC is to provide contracting opportunities for the private sector since we receive funding from the federal government. This leveling project was to be contracted out so when deciding what equipment to use, it was decided to use the newer electronic digital leveling equipment since it is commonly in use by the private sector and would provide a broader opportunity for respondents. Both of these first two decisions had details that later had to be worked out with NGS and will be detailed below.

A major determining factor in selecting the stations to level was proximity to existing NAVD88 first order benchmarks. Searches of the NGS database were done to determine the number of first-order adjusted benchmarks within a two mile radius of the station. Stations were selected that had at least 4 or more benchmarks within the two mile radius, knowing that in some cases the elevations would have changed over the years and that leveling would have to be extended to check into additional benchmark(s) to meet the specifications.

Along with proximity of the benchmarks, site accessibility/condition and elevation difference were also reviewed. Several sites were originally accepted based on proximity of benchmarks and network geometry, but later had to be rejected based on the severe elevation difference, and therefore, expense, to level to the site. Another seemingly suitable site was rejected due to frequent vandalism, which put into question the long-


term viability of the site as part of the network. Stations were also reviewed for known subsidence issues in their area and one station was rejected based on that issue.

It was decided that each station was to be the Wyatt drilled-braced monument with choke ring antenna with radome that were installed by the SCIGN group (SCIGN web site). These stations have been shown to have the best stability, with the least measurement noise (Williams et al, 2004). Stations installed in the earlier years of the SCIGN project had less rigorously designed monuments and were used in only a few cases where there was not a more suitable monument available (VTIS, VNDP and VNPS). Each station’s vertical time series was reviewed to select those stations that had the lowest RMS values. Stations with RMS ≤ 5mm in the vertical were selected.

Geometry of the network was a major consideration, so after stations were evaluated on all the above criteria, they were chosen to provide 80 km spacing over the 10 counties (or as close to that as possible) with the qualified stations. After evaluating these issues and the estimated cost on a station by station basis, the following 20 stations were chosen and are shown in Figure No. 1.

1. CRBT – Camp Roberts, Monterey CountyVersion 1.10 (October 28, 2004) of 375/4/2023 2:33 PM

Figure No. 1. Map showing CGPS Stations included in leveling contract.

2. USLO – Cal Poly State University, San Luis Obispo County3. VNDP – Vandenberg Air Force Base, Santa Barbara County4. COPR – Coal Point Oil Reserve, Santa Barbara County5. BVPP - Buena Vista Pumping Plant, Kern County6. RSTP – Rosamond Treatment Plant, Kern County7. CCCC - Cerro Coso Community College, Kern County8. LVMS – Lockwood Valley Maintenance Station, Ventura County9. TOST – Thousand Oaks Sheriff Station, Ventura County10. VNPS – Vincent Pump Station, Los Angeles County11. VNCX – Van Norman Complex, Los Angeles County12. ELSC – East Los Angeles Science Center, Los Angeles County13. VTIS – Marine Exchange, Los Angeles County14. BSRY – Barstow Road Yard, San Bernardino County15. BKAP – Baker Airport, San Bernardino County16. NDAP – Needles Airport, San Bernardino County17. MVFD– Montezuma Valley Fire Department, San Diego County18. NSSS – Naval Space Surveillance Station, San Diego County19. GLRS – Galeano Reservoir, Imperial County20. IID2 – Imperial Irrigation District, Drop 2, Imperial County

Selection of Leveling Specifications

As stated above, we needed to achieve final elevations that would be accurate enough to use as vertical control in the orthometric height adjustment to provide final GPS derived orthometric heights at the ±2 cm level. We had to evaluate several factors to determine what specification to follow. While we would have liked to achieve the vertical accuracy provided by First Order leveling, we had to consider the high cost of this type of leveling and the fact that few consultants would have the expertise or equipment to perform this type leveling, and would therefore limit the response to our contract. Another limitation we had to consider was the allotted budget amount for this project. We decided to use the FGCS specification for Second Order, Class II leveling to provide final positional accuracies of our elevations in the 5mm range at 95% confidence level and to allow for the most number of stations to be leveled to with the amount of funding available. We felt this specification would also open the contract up to more consultants since the equipment needed would be more commonly in use than that required for First Order leveling.

Modifications to FGCS specifications

The CSRC did a review of the FCGS specifications (1994) in an effort to clarify the methods to be used to level to CGPS stations. In an effort to be as efficient as possible, and to get the most from a limited budget, we worked with NGS to create a modified specification to use for this leveling project. We started with the FGCS Second Order, Class II specification and made the following modifications with NGS approval.


1. We would perform a single run benchmark check between two NGS published, First Order benchmarks that had to agree with the specifications definition of a valid check connection (in our case, 8mm times the square root of the shortest one way distance). If we didn’t meet this valid check connection, we would run to another benchmark until we had a valid benchmark check connection. Checking into one benchmark at each end of the leveling run was a change from the FGCS specification that calls for two at each end.

2. The level run to the CGPS had to be double run, either from one benchmark and back or from one benchmark to the CGPS station and then to the other benchmark.

3. We had to keep the length of the leveling line from each valid benchmark to the CGPS at 10 km or less.

4. We were not going to set any interim benchmarks, but had to use stable pins or turning pucks for all turns and/or temporary benchmarks.

These modifications and other suggestions and clarification for field work for this project were written up in a document titled CSRC Specifications and Procedures for Second Order, Class II Geodetic Leveling to Establish Elevations on CORS (dated March 10, 2003) and was included as part of the contract documents. It has also been posted on the CSRC web site for other users. It is included as Appendix A to this paper.

Determining Methods to Measure to GRM, BPA and ARD

When designing this leveling project, discussions were held to determine the best method for measuring to the geodetic reference mark (GRM) and the base of the pre-amp (BPA) of the antenna, with the least amount of disruption of the data/GPS signal. The original idea was to remove the radome, the antenna and the top half of the SCIGN adaptor (SCIGN, 1999 a) to level directly on the GRM. It was decided that this method would cause too much disruption of the equipment and GPS signal. An alternative method was derived that would give us the measurements needed to calculate all elevations required.

Each CGPS has a reference mark or divot (ARD) on one of the tripod legs. This mark was created as part of the original installation contract of the Wyatt drilled-braced monument installations (CSRC, 2003). (A similar mark was created on the other types of monument installations for

use in this leveling project.) The leveling project would establish an elevation on each of


Figure No. 2. Typical SCIGN antenna.

these ARD using the electronic leveling equipment. From this ARD mark, a manual measurement (using a steel rule) would be made up to the bottom of the antenna adaptor, which can be accessed from the underside of the tripod/antenna connection. Then the radome would be removed which allows access to measure from the bottom of the adaptor to the top of the adaptor. This measurement was to be done in each of the cardinal directions, in both meters and feet (for a check), and then averaged to determine the adaptor height. These measurements allow for calculation of the GRM and BPA elevations, based on the machining specifications of the adaptors (SCIGN, 1999), and are able to be completed in a few minutes for minimized disruption of the GPS data. The following general formulas are used to determine the elevations:

Leveled ARD elevation + distance to bottom adaptor + adaptor height = BPA elevation

BPA calculated elevation – 0.0083 meters = GRM elevation (with SCIGN adaptor)

The time of removal and replacement of the radome was to be recorded for use by SOPAC/SCIGN to track any anomalies in the data.

Field Project Mobilization (after issuance of contract)

Once the final sites were determined, site contact personnel were notified of the pending survey. This proved to be more of an issue than initially expected due to the fact that many of the on-site contacts listed in the SCIGN database had retired or moved on since last contacted by any of the CGPS network personnel.

Field note forms to be used in the reconnaissance phase were prepared. Two different forms were prepared. The first form was designed for use in recording the site condition and the measurements necessary to determine the height difference from the antenna reference divot (ARD), which is generally a punch mark on the leg of the CGPS tripod. Additionally, this form was used to record the surveyor, date, the time of removal and reinstallation of the radome, the antenna make and the antenna serial number (see Appendix B for example).

The second reconnaissance form was designed to record the condition of the found benchmark monuments (see Appendix C for example). These note sheets had blanks for recording the NGS permanent identification numbers (PID) of the marks and the stampings of the marks. The form provided blanks for latitude and longitude of the mark as determined by handheld GPS, suitability for use of the mark by GPS, and space for any notes thought necessary by the field surveyor to show changes from the NGS records, or any other data that might be pertinent to the project. Additionally, space was provided for the field surveyor to note his idea of the most logical route of leveling from the nearest located bench mark to the subject CGPS station. A location on the form was also provided to note the date that the field data was transmitted to the NGS via the NGS Online Recovery Program.


A digital map file was prepared for each site showing the CGPS location as well as the NGS record location of the nearest five bench marks (see Appendix D for example). This allowed our field surveyors to drive directly to the area and to the best available record location of the bench marks using GPS navigation and moving map technology. In addition to the map, NGS data sheets were obtained via the NGS website for all of the known bench marks near the CGPS sites. These were furnished to the field surveyors in both printed and digital format for their use in locating, identifying, and verifying the existence and usability of the vertical control in the area. All necessary changes to the NGS records, along with the handheld GPS positions, which were derived from the reconnaissance operation, were transmitted to the NGS for incorporation into the National Geodetic Survey database via the NGS Online Recovery System.

Field Leveling

The following is the initial leveling instructions and procedures to field crews:

Main Idea for Field Leveling:At each CGPS site, level from the nearest NGS 1st order NAVD88 benchmark to the antenna reference divot (ARD) (“punch mark”) on the CGPS “tripod” leg or base, following the Second Order, Class II CSRC Modified Specification (Appendix A). This specification details the process of a double run (closed loop) from the benchmark to the CGPS site with an additional single run to a second 1st order benchmark for a check.

Recommended Equipment:Leica NA 3003 Digital Level (with Version 3.3 firmware or higher) or equivalentCertified one piece bar code rods, with the stays (recommended)Stiff leg tripod Turning pucksTurning drive pins Steel rule, calibrated in meters and feet

Field Procedures:1. Calibration (collimation of level) to be accomplished once per day and the result

entered into the level and used until the next calibration.2. When using turning pucks for turn point, make sure personnel handling the rod are

trained to step on the puck to assure that it is down as far as it will go and completely stable during the turn. Also make sure any drive pins set for turns are completely stable.

3. Maximum site length not to exceed 60 meters (Leica level specification)4. Backsight/Foresight balance to be not more than 10 meters per setup and 10 meters

accumulated per section.5. Designate one rod as “A” Rod, use an even number of turns per section to make sure

you take off the bench with “A” Rod and get back on the next bench with the same “A” Rod.


6. Maximum difference between forward and backward running of the double run lines not to exceed 8mm times the square root of the shortest one way length of section in kilometers.

7. Maximum difference between record elevation difference and single run difference to verification bench to also be less than 8mm times the square root of the shortest one way length of section in kilometers. If first run between benches does not pass, run back to the initial bench. If your two runs match each other to the above spec but still do not match the record, you must run to further benches.

8. If any runs/sections are more than 3 kilometers, set a drive pin as a temporary bench to make sections 3 km or less in length, in order to isolate any errors and minimize the amount of reruns necessary to correct any errors.

9. The last turn into the ARD will have to be made with the “A” Rod on the turning puck and the stainless steel 6” ruler read with the optical cross hair and hand entered into the gun. Make this a short turn with about a 5-10 meter sight distance (far enough away to focus, but as close as possible to negate any inaccuracies in the optical reading) (see Figure No. 3).Turning back out from the ARD would be just the opposite of the above.

10. For verification of the benchmark elevations in the field, it is a good idea to have previously run the planned benchmarks through the NGS program LVL_DH (Shields, 2003), to determine the elevation difference that takes the gravity correction out of the published difference to give a difference that should match raw leveling. This is the difference that we are trying to match.

11. Review guidelines for NGS project submittals regarding field raw data file. There are specific guidelines for recording the temperatures at the beginning and end of a section, the instrument person, the time of leveling, etc. Also the curvature function should be turned off in the level and the data should be collected in meters. Appendix A has some of this information, with additional references to help determine the correct field data file collection methods.

12. A unique identifier should be assigned to each mark to be elevated. The last four numbers of the NGS PID could possibly be utilized for the BM’s. Other marks should be identified so to avoid identical numbers in other sections of the leveling project.


Radome removal and BPA measurement training1. At each CGPS, measure two vertical distances – a) from the reference mark on the

CGPS leg to the bottom of the CGPS antenna adaptor and b) from the bottom of the adaptor to the top of the adaptor – all in accordance with CSRC procedures. The vertical distance from the bottom to the top of the adaptor shall be the average of four measurements at different locations, approximately 90 degrees apart, around the adaptor. All measurements shall be made to the nearest millimeter and shall be accurate to plus or minus one millimeter.

2. Each measurement shall be verified by re-measuring with a measuring device graduated in feet. Only measurements that have agreement between the metric and foot measurements of one millimeter or less shall be accepted.

3. The field notes shall show and document all GRM measurements. To make the GRM measurements, it is necessary to remove the CGPS radome to provide access to the CGPS antenna adaptor.

4. Under no circumstances remove, adjust, or manipulate the CGPS antenna. 5. Use care in the removal and reinstallation of the CGPS radomes. Prior to removing

each radome, note and mark the position of the radome. When the GRM measurements for each CGPS are completed, immediately reinstall the radome in the exact position as originally installed (for instructions, see SCIGN, 1999 b & c).


Figure No. 3. Last turn into ARD is read optically from level (left) to steel rule held at ARD (right) and manually entered into level for recordation in raw data digital file.

Figure No. 4. Manual measurement from ARD to bottom of antenna adaptor (left) and from bottom of antenna adaptor to BPA (right).

Figure No. 5. Leveling equipment used – Leica NA3003, Invar staffs with stays, stiff leg tripod.

Equipment Used

For the differential level measurements necessary for this project the following equipment was used:

Leica NA3003 Digital Level, SN 91716 with recent service record

Leica Invar Geodetic 3 Meter Leveling Staff GPCL3, SN 22962 with calibration certificate

Leica Invar Geodetic 3 Meter Leveling Staff GPCL3, SN 23219 with calibration certificate

In addition to the above major equipment, both rods were equipped with stays, to hold the rod plumb and stable while being read, and dual level bubbles to assure that neither bubble had

become out of level during the survey. Kern leveling turtles (pucks) were utilized for solid, stable, but portable, turning points. The same equipment was used during the entire project (see Figure No. 5 for example).

Specification and Equipment Issues during Initial Field Work and Office Processing

Once field leveling started, we realized we apparently weren’t meeting the specification criteria of 0.1mm standard deviation for each measurement. To achieve a value of 0.1mm for a measurement, we had to use sight lengths of 25 – 30m, even though the FGCS specifications allow a much longer sight length for Second Order, Class II. It was unclear in the FGCS specifications if this was to be 0.1mm standard deviation of “a reading” (=± (r2/(n-1))) or of the “mean of three readings” (standard deviation of the mean = m=±/n). It was also unclear at first what was being recorded in the Leica digital leveling file. We called both NGS and Leica to get verification of what we were trying to achieve and what we were achieving, respectively. We got a final determination from the NGS that this specification is supposed to be the standard deviation of the mean even though the FGCS document (1994 version) is not clear on this. From Leica we got clarification that when running in the mean mode on their Version 3.3 firmware, the standard deviation being reported in the raw data file was the standard deviation of the last single reading and not the standard deviation of the mean of the number of readings taken. They also gave us guidance on how to use their “Mean Mode with Entered Std


Dev” to assure that we were meeting the 0.1 mm specification for the mean of three measurements. This information from Leica meant that an update to the digital level firmware was needed since we were using an older version (Version 3.2) that didn’t have this functionality. After the upgrade, we set the level to record in the “Mean Mode with Entered Std Dev”, which allows the level to record only when it attains an acceptable standard deviation of the mean. The level firmware allows for entering of a standard deviation for 20 m sight length. Internally, the level computes the standard deviation for the length of sight being taken by use of a straight-line proportion, i.e., if set to 0.03mm@20m the level will accept 0.09mm@60m. Since the level will not physically read a sight length longer than 60 meters, it will never accept a set of readings that are outside of 0.09mm standard deviation. Using this mode, we were able to complete the second half of the project using 50± meter sight lengths and still obtain the same closure accuracies that we attained in the first half of the project using 25 meter sight lengths, and in a much more efficient manner.

The criteria stating a 0.1mm standard deviation for three measurements was the most problematic specification to meet in the field and the following are the changes/improvements to our field procedure that we made to meet this specification (after updating to the version of Leica firmware with the necessary capabilities).

1. Set your level to run in the mean mode with the standard deviation set to 0.03mm for 20 meters and keep your sight distances in the 40 to 60 meter range.

2. Watch the standard deviation as field measurements are taken to verify that it is improving with additional measurements and that it meets the specification of 0.1 mm standard deviation of the mean when recorded. (In the office, you will not be able to verify this by looking at the 52 record in the raw file for each foresight measurement accepted. For example, in the Leica raw file “52..0003+010” means 3 measurements were taken in the field and the last one resulted in a standard deviation of 0.1mm. The standard deviation of a single measurement is reported in the data file, no matter which mode you are using to run the level.) Refer to your level manual for the details of the values recorded and the code explanations.

3. Alternatively, set your tolerance for 0.04mm for 20 meters and keep your sighting distances less than or at 50 meters. Set this way, the instrument will not record a measurement that would exceed the specification of 0.1mm standard deviation of the mean.

4. Try to perform leveling in temperatures less than 90 degrees.5. Keep instrument shaded during measurements.6. Verify that rod is absolutely stable when measurements are being taken.7. If not meeting the standard deviation on a particular shot, try the measurement with a

shorter sight distance to see if standard deviation improves (which would indicate an atmospheric condition between rod and instrument). If it doesn’t improve, problem is probably at instrument so you will need to check for settling of instrument, vibrations of instrument (from road, wind, etc), or if the instrument is not shaded and possibly too hot. Failure to achieve the standard deviation specification of a particular set of measurements is an indication that the level is not able to resolve the measurement precisely.


Rod stays were not initially required, but by experience, made meeting this specification much easier by eliminating rod movement (allowed for meeting measurement standard deviation at somewhat longer sighting distances than would otherwise be possible). By experience, the sight distance is usually in the 35 to 50 meter range to meet all the required specifications (especially the standard deviation of the measurements). Additionally it should be noted for future surveys, that the firmware for the digital level to be utilized, must be studied to verify that the algorithm being used and stored in the level, meets the specification criteria. (The FGCS specifications (FGCS, 2004) have been updated to reflect the standard deviation of the mean clarification.)


Field verification of level run closure/specifications met

At

each of the 20 CGPS sites, we leveled from the nearest existing bench mark to the 2nd nearest existing bench mark using the above mentioned FGCS Second Order, Class II Specifications (2004; NGS revised version 4.1; now using std. dev of the mean) and CSRC specifications (Appendix A). The field-derived difference in elevation was compared to the published difference in elevation after removing the orthometric corrections using the NGS program LVL_DH. If the run between the benchmarks matched the published difference within the specification tolerance of 8 mm times the square root of the shortest one-way leveled distance between the two benchmarks, the benchmarks were considered validated.

If the field leveled, single run difference did not match, the crew leveled back from bench 2 to bench 1 to verify the loop misclosure of the field leveling. If the verification run matched the single run (which they did in all cases), then we continued to level to more distant existing bench marks until such time as we found two existing bench marks between which our field leveling matched the record difference within the stated tolerance (see Table No. 1 for example).

Once, we had two “validated” benchmarks, we ran from the nearest validated bench to the CGPS, along the nearest and flattest route available. As per the CSRC specifications (Appendix A), we used drive pins as temporary bench marks along any route that was more than 3 km to the CGPS to break the run into “sections” of less than 3 km. At the


Table No. 1 Sample Benchmark Elevation Checks/Verification

CGPS FROM TO HT DIFF (m)DIST (km)

NAVD88 Diff

LVL_DH Corrected

Diff

MAX Allowed

MisclosureSingle Run Misclosure

Double Run

Misclosure

BKAP FT1138 FT0056 -2.4992 1479 -2.501 -2.501 0.010 0.002

BSRY EV0028 EV0027 -2.9437 206 -2.940 -2.939 0.004 -0.005

EV0027 EV0028 2.9434 206 2.940 2.939 0.004 0.004 -0.0003

EV0027 EV0044 5.8967 1139 5.895 5.897 0.009 0.000

BVPP FU2195 FU2197 -1.9412 85 -1.935 -1.935 0.002 -0.006

FU2197 FU2195 1.9403 85 1.935 1.935 0.002 0.005 -0.0008

FU2195 FU3245 25.7484 1305 25.771 25.771 0.009 -0.023

FU3245 FU2195 -25.7493 1303 -25.771 -25.771 0.009 0.022 -0.0009

FU2191 FU3245 -22.2549 906 -22.259 -22.259 0.008 0.004

CCCC FT0640 FT0638 -16.8391 1566 -16.842 -16.837 0.010 -0.002

COPR EW3794 EW3793 -17.9157 1393 -17.920 -17.920 0.009 0.004

EW3793 AE4854 -2.6773 981 -37.348 N/A 0.008 34.671

AE4854 EW3793 2.6766 978 37.348 N/A 0.008 -34.671 -0.0007

CRBT FV0260 FV0203 -9.0498 1614 -9.048 -9.048 0.010 -0.002

CGPS, we used a small stainless steel ruler graduated in millimeters (Westcott 10414) as the last rod shot to the ARD point on the CGPS tripod leg. After turning into the CGPS, we ran back from the CGPS to the starting bench along the same route, using the same specs, and across the same temporary benchmarks. The forward run was compared to the return run to assure that we again matched the specified tolerance of 8 mm times the square root of the kilometers. In all cases our results matched well within the allowable tolerance (see Table No. 2 for example).

Table No. 2. Double Run Closures from Validated Benchmarks to CGPS ARD.

CGPS SITE FROM TO

Height Difference

(m)

Single Run Distance

(m)

Double Run

Closure

Maximum Allowable Closure

BKAP FT1138 BKAP ARD -1.31269 1137BKAP ARD FT1138 1.31135 1134 -0.001 0.009

BSRY EV0044 BSRY ARD -2.45185 1193BSRY ARD EV0044 2.45104 1193 -0.001 0.009

BVPP FU2197 BVPP ARD -69.28625 8698BVPP ARD FU2197 69.29930 8695 0.013 0.024

CCCC FT0638 CCCC ARD -82.62379 3661CCCC ARD FT0638 82.62162 3656 -0.002 0.015

COPR EW3793 COPR ARD -15.02212 3793COPR ARD EW3793 15.02446 3790 0.002 0.016

CRBT EV0260 CRBT ARD 53.40328 1310CRBT ARD EV0260 -53.40316 1309 0.000 0.009

Office Procedures

As the field leveling was completed to each site, the raw data file was downloaded from the level using the proprietary download software. The raw field data was reviewed for quality control and processed to perform a preliminary adjustment of the data. After the preliminary analysis and quality control was complete, preparation of files for submittal to NGS for publication of the elevations were completed.

Several programs were used for the handling of the leveling data. In addition to the proprietary download program (that usually comes with the purchase of the level), a program called StarNetPro was used to process the raw data file and adjust the extracted elevation differences. A program called NABOOK was used to create a field book file that was used to find errors and data that did not meet specifications. (Be aware that the program may incorrectly flag standard deviation, as standard deviation of the mean.) This program also is used to create some of the files needed for the NGS publication process. The following is a simplified outline of the usual procedure, but the process is described in detail in Appendix E:


Initial data processing and quality control:1. Download digital raw data file from level using proprietary software.2. Review the ASCII raw data file for input errors and needed revisions.3. Using a utility called NA3000, extract the elevation differences and distances for

adjustment in StarNetPro.4. Using StarNetPro, run a preliminary adjustment of the data for quality control.5. Once quality control has been completed on raw data file, it is ready for NGS

submittal preparation.

Preparation of files required for NGS data submittal process is a complex process and requires familiarity with several documents and programs. For detailed instructions of the submittal process, refer to the documentation Murray (1999), NGS (1992) and the NGS web site. We have detailed the process we followed (in conjunction with these other documents) in Appendix E.

Summary

At two locations, we had problems validating benchmarks. Those locations were at the Buena Vista Pumping Plant station (BVPP; 158 meters) and at the Rosamond Treatment Plant station (RSTP; 745 meters). Unknown to us prior to the project, both of these stations are near the edges of known subsidence areas. At the BVPP site, we had to level to four existing benchmarks, instead of the normal two, before we found two that would agree with the record differences within Second Order, Class II tolerances. At the Rosamond Site, we leveled to five benchmarks before finding two that would agree within the project tolerances.

The resulting elevation determined at the geodetic reference mark (GRM) by leveling at BVPP is 20 cm higher than the height for that same mark determined from the CSRC published ellipsoid height, minus the geoid height determined from NGS’ current geoid model (Geoid 03), which could be explained by equally subsiding benchmarks. However, at RSTP, where we actually had more trouble validating benchmarks, the same difference is only 4cm, which is not that much different than many of the other sites within the project.

At the Montezuma Valley Fire Department CGPS station (MVFD) in San Diego County, we had no trouble validating benchmarks, but the difference between the leveled GRM height and the same height determined from the ellipsoid height and Geoid 03 miss-matches by 11 cm. This site is located in Montezuma Valley at 1220 meters elevation in San Diego Co. (The only NAVD88 benchmarks in this area were third-order.)

We find a similar situation at Galeano Reservoir CGPS (GLRS) near the Salton Sea in Imperial County, where the benchmarks fit each other, but the result misses by 12cm. This region is known for subsidence, so all of the benchmarks may have experienced the same magnitude of subsidence.


Acknowledgements

The authors would like to acknowledge the assistance of Dave Zilkowski, Dale Pursell and others at NGS who worked with the CSRC to modify and clarify the FGCS specifications for this type of leveling. We also appreciate the assistance of Orland Murray, Charles Whalen and Kathy Koepsell with the NGS “blue booking” process. Special thanks go to the leveling crews from Johnson-Frank & Associates and Riverside County Flood Control District for their patience, perseverance and assistance with implementing and trouble-shooting these procedures and assuring that the project specifications were met.

References

California Spatial Reference Center (CSRC) (2004). “Scripps Epoch Coordinate Tool and Online Resource (SECTOR)”. R. Nikolaides, “Observation of Geodetic and Seismic Deformation with the Global Positioning System, Ph.D. thesis, University of California, San Diego”, 2002. http://sopac.ucsd.edu/processing/refinedCoordsDoc.html

California Spatial Reference Center (CSRC) (2003). SCIGN GPS Site Monument Information. http://csrc.ucsd.edu/howTo/SCIGNMonumentInfo.html

California Spatial Reference Center (CSRC) (2002). “A Master Plan for a Modern California Geodetic Control Network – A Plan to Implement the National Height Modernization Program Goals in California”. Scripps Institute of Oceanography, University of California, San Diego, October 18, 2002. http://csrc.ucsd.edu/input/csrc/csrcMasterPlan.pdf

Federal Geodetic Control Subcommittee (FGCS) (5/27/2004). “FGCS Specifications and Procedures to Incorporate Electronic Digital/Bar-Code Leveling Systems, Version 4.1”. http://www.ngs.noaa.gov/FGCS/tech_pub/Fgcsvert.v41.specs.pdf

Federal Geodetic Control Subcommittee (FGCS) (6/14/1994). “FGCS Specifications and Procedures to Incorporate Electronic Digital/Bar-Code Leveling Systems, Version 4.0”. http://www.ngs.noaa.gov/FGCS/tech_pub/Fgcsvert.v40.specs.pdf

Leica Geosystems (1996). NA2002/NA3003 Version 3.2/3.3 Instrument Manual.

Hudnut, Kenneth W., Yehuda Bock, John E. Galetzka, Frank H. Webb, and William H. Young (2001). "The Southern California Integrated GPS Network (SCIGN)." Proceedings of Commission 6, of the International Federation of Surveyors, Deformation Working Group, 10th International Symposium on Deformation Measurements, Orange, California, USA, pp. 129 to 148.

Murray, Orland W. (1999). “Digital Leveling User’s Guide – Using the Leica NA Series of Digital Levels in Accordance with FGCS Specifications and the Input Formats and Specifications of the National Geodetic Survey Data Base”. (NOAA Document)


http://www.ngs.noaa.gov/FGCS/tech_pub/Fgcsvert.v41.specs.pdf


http://csrc.ucsd.edu/input/csrc/csrcMasterPlan.pdf

http://csrc.ucsd.edu/howTo/SCIGNMonumentInfo.html

http://sopac.ucsd.edu/processing/refinedCoordsDoc.html

National Geodetic Survey (NGS) (1992). “Vertical Control Field Data Processing System, Version 3.00”. National Oceanic and Atmospheric Administration, Charting and Geodetic Services, National Geodetic Survey Division.

SCIGN (1999). Antenna adaptor design and specification drawings.a.) http://pasadena.wr.usgs.gov/scign/group/dome/adaptor.htmlb.) http://pasadena.wr.usgs.gov/scign/group/dome/instr_short.htmlc.) http://pasadena.wr.usgs.gov/scign/group/dome/instr_tall.html

Shields, Rene (2003). “LVL_DH and Tidal and Orthometric Elevations”. Professional Surveyor, July 2003, page 31. http://www.ngs.noaa.gov/TOOLS/LVLDH/lvldh.shtml

Snay, Richard (2003). “Horizontal Time Dependent Positioning”. Professional Surveyor, November 2003, pages 30 -34.

Snay, Richard (1999). “Using the HTDP Software to Transform Spatial Coordinates Across Time and Between Reference Frames”. Surveying and Land Information Systems, Vol. 59, No. 1, 1999, pages 15-25. http://www.ngs.noaa.gov/CORS/utilities3/

Williams, S.D.P., Y. Bock, P. Fang, P. Jamason, R.M. Nikolaidis, L. Prawirodirdjo, M. Miller, D.J. Johnson (2004). “Error Analysis of Continuous GPS Position Time Series”. Journal of Geophysical Research, 109 (B03412), doi: 10.1029/2003JB0022741, 2004.

Zilkoski, David B., Edward E. Carlson and Curtis L. Smith (2003). “Guidelines for Establishing GPS Derived Orthometric Heights, 2 cm and 5 cm Standards, Draft Version 1.4”. NOAA Technical Memorandum, NOS NGS-59, Silver Springs, Maryland, USA.

Zilkoski, David B., Joseph D. D’Onofrio and Stephen J. Frakes (Nov 1997). “Guidelines for Establishing GPS Derived Ellipsoid Heights, 2 cm and 5 cm Standards, Version 4.3”. NOAA Technical Memorandum, NOS NGS-58, Silver Springs, Maryland, USA. http://www.ngs.noaa.gov/PUBS_LIB/NGS-58.html

Web Site References

NGS Web Site: http://www.ngs.noaa.gov/

SCIGN Web Site: http://www.scign.org/

SOPAC Web Site: http://sopac.ucsd.edu/

CSRC Web Site: http://csrc.ucsd.edu


http://csrc.ucsd.edu/

ftp://lox.ucsd.edu/

http://www-socal.wr.usgs.gov/SCIGN

http://www.ngs.noaa.gov/PUBS_LIB/NGS-58.html

http://pasadena.wr.usgs.gov/scign/group/dome/instr_tall.html

http://pasadena.wr.usgs.gov/scign/group/dome/instr_short.html

http://pasadena.wr.usgs.gov/scign/group/dome/adaptor.html

Appendix A – CSRC Specifications and Procedures document (as originally issued)

Specifications and Procedures for Second Order, Class II Geodetic Leveling to Establish Elevations on CORS

(within 10 km of valid vertical control and using digital/electronic bar-code leveling systems)

March 10, 2003

1. Description: These specifications and procedures specify the requirements for performing second order, class II geodetic leveling, using electronic digital/bar-code leveling systems, to establish elevations on continuously operating reference stations (CORS). The application of these specifications and procedures is limited to establishing elevations on CORS that are within 10 km of a valid vertical control station.

2. Requirements: The leveling work shall conform to the second order, class II specifications and procedures specified in the Federal Geodetic Control Subcommittee (FGCS) document entitled “FGCS Specifications and Procedures to Incorporate Electronic Digital/Bar-Code Leveling Systems,” adopted June 14, 1995, and the requirements specified in this document. The referenced FGCS document is referred to as the “FGCS Specifications” hereafter. This document is available from the National Geodetic Survey (NGS) website at “http://www.ngs.noaa.gov/FGCS/tech_pub/FGCSvert.v40.specs.pdf.” The FGCS Specifications shall apply unless specifically superseded by the requirements specified below. If there is a conflict between the FGCS Specifications and this document for a given specification or procedure, this document shall take priority.

3. Network Geometry:a. Bench Marks – Bench marks are not required to be set. However, temporary

bench marks that are suitable for the purpose intended shall be set in accordance with the spacing specified for bench marks in the FGCS Specifications. The temporary bench marks divide the leveling line into sections for these specifications and procedures.

b. Bench Mark Ties – The minimum bench mark tie shall be one valid bench mark (vertical control station) conforming to the specifications below.

c. Valid Bench Mark – A valid bench mark shall conform to the following:i. Each valid bench mark shall have a NGS-published, second-order, class II (or

better) adjusted NAVD88 elevation value. Priority shall be given to those bench marks that are included in the California High Precision Geodetic Network.

ii. Each valid bench mark shall have an acceptable “check connection” with an adjacent second-order, class II (or better) bench mark having an adjusted published NAVD88 elevation value. The check connection shall be run either a) from the valid bench mark directly to an adjacent bench mark or b) from the



CORS to a bench mark adjacent to the valid bench mark. The allowable tolerance limit for a check connection shall be 8 mm times the square root of the shortest one-way distance of the check connection, in kilometers, (8√L). Note: The FGCS Specifications permit check connections to be single run.

iii. The length of the leveling line from each valid bench mark to the applicable CORS shall be 10 km or less.

d. Connections to Other Network Control Points – Other than specified above, connections to other network control points are not required.

4. Instrumentation:a. Leveling System – An electronic digital/bar-code leveling system shall be

used for all leveling work. The leveling system shall be in good condition and shall have been serviced, by an authorized service center, within the last six months.

b. Instrument Tripod – The instrument tripod shall have non-adjustable legs (fixed-length legs).

c. Temporary Bench Marks – Temporary bench marks shall be driven steel, turning pins similar to the turning pins utilized by NGS or an acceptable equivalent. A suitable driving cap shall be utilized when driving the pins.

d. Turning Points – The use of steel turning pins and turtles is not required for turning points but is recommended. Turning points shall be stable points and suitable for the leveling work being performed.

e. Bipods – The use of bipods to provide stable rod plumbing is recommended but not required.

f. Umbrella – The use of an umbrella to shade the leveling instrument is not required unless recommended by the instrument manufacturer. In other cases, the use of an umbrella to shade the instrument from a bright sun is recommended.

5. Calibration Procedures: a. Collimation Time Interval – The time interval between collimation error

determinations shall not be longer than one day for all leveling instruments. This information shall be recorded as part of the leveling raw dataset.

6. Field Procedures: a. Minimal Observation Method – The “electronic digital/bar-code” leveling

method shall be used for all leveling work.b. Section Running – The “double run” leveling procedure shall be used to

perform the leveling from the valid bench mark to the CORS.

7. Office Procedures: The paragraph in the FGCS Specifications, under Office Procedures, regarding normalized residuals and least squares adjustments models does not apply to this leveling work, except the superscript footnote “n” for collimation error shall apply.


(end)


Appendix B – CSRC Antenna Measurement Form

Example of completed form for a CGPS site.


Appendix C – CSRC Benchmark Reconnaissance Form

Example of completed form for the benchmarks for the level runs to a CGPS site.


Appendix D – CSRC Site Leveling Plan

Example of leveling plan for a CGPS site.


Appendix E - Data Processing For NGS Vertical Project Submission

Once the raw leveling data file is collected from the field, it needs to be properly formatted and processed for submission to be included in the NGS database (a process that is commonly called “blue booking”). The guidelines in the next sections will step through this process, which utilizes three NGS program suites, NABOOK, VFPROC, and WDDPROC. (The NABOOK program has to be purchased by the user; the VFPROC and WDDPROC programs are free on the web site, but the documentation for it has to be purchased by the user.) The VFPROC programs are DOS-based, but NGS has been working to convert them to Windows-based programs. These Windows–based programs are recommended over the DOS-based suite, because of better ease of use. The use of the Windows versions will be described here.

The project managers and field crews need to be familiar with the documentation for these programs, in addition to the NGS guidelines for vertical project submission, and of course the FCGS specifications and the documentation for their equipment, before starting any field work. (The documentation for NABOOK, called DvlGuide, is very useful and has straightforward instructions for preparation and method for leveling).The purpose of this Appendix is not to replace these other documents, but to help clarify and highlight some of the items to pay attention to that will help the whole process move smoothly.

Although there are several digital/electronic level manufacturers, the projects completed so far, which are therefore the basis of this document, were all completed utilizing Leica electronic levels (NA3003 and DNA03 models). These guidelines will address some items specific to the Leica equipment, but overall the general process will be the same with all brands of digital/electronic level. The CSRC is not endorsing any particular brand of level.

Raw Level Data File PreparationSince the vertical project will be processed according to NABOOK/VFPROC guidelines, this means it will probably be necessary to edit the raw digital level files so that NABOOK will be able to read the file. The documentation for the level utilized can be used to help understand the contents of the raw file. Currently, NABOOK does not understand the data file format produced by the new Leica DNA03 digital level. It does understand the data format produced by the older Leica NA3003 automatic level. It is possible to convert the DNA03 files (typically given the suffix *.GSI) to the older NA3003 files (typically given the suffix *.RAW) using a file conversion program (DnaGsiConverter.exe) available from Leica.

The raw file represents not only the observations made during the level circuit, but also special codes punched into the level by the Instrument Operator. The NABOOK documentation specifies exactly which buttons to punch, and which data items to enter into the gun. If the raw file you’re working with doesn’t have these codes properly entered, it will be necessary to convert them.



http://www.ngs.noaa.gov/FGCS/BlueBook/

http://www.ngs.noaa.gov/PC_PROD/pc_prod.shtml#WDDPROC

http://www.ngs.noaa.gov/PC_PROD/pc_prod.shtml#VFPROC

In the Leica raw format, the first entry in the raw file is usually a specification as to whether the levels are being run in single-run (backsight/foresight) mode or double-simultaneous-run (backsight/foresight/foresight/backsight) mode. In this example, the number “1” indicates single-run leveling:

410002+?......1

The number “2” indicates double-simultaneous leveling (410001+?......2),and this is not permitted by NABOOK, even though it is a valid FGCS procedure for precise leveling. If double-simultaneous levels were run, the data file will have to be converted, with some effort, to single-run leveling. The double-simultaneous format (usually called BFFB leveling) appears like this in the raw data file:

110017+00000379 32..00+00037590 331168+00132005 52..08+0003+024 110018+00000380 32..00+00037140 332168+00210094 52..08+0004+029 110019+00000380 32..00+00037110 336168+00210919 52..08+0003+013 110020+00000379 32..00+00037630 335168+00132849 52..08+0003+012

What you see here are four consecutive rod readings. Files of this type must be converted, with some labor, into the files that NABOOK can read. This can be done, by extracting the second pair of rod readings, and inserting them into a new, although fictitious, level run which happens to have been run simultaneously with the first. However, because of the labor involved (this really should be done using specially-designed software) and extreme amount of data manipulation, this procedure won’t be discussed further here. Future projects to be submitted for CSRC data processing should not be leveled using this method.

As another example of procedural issues, Caltrans has used slightly different data-entry routines than as required by NABOOK. The following table was provided by Caltrans, and compares the Caltrans procedures versus the NABOOK procedures.


Each of these “Codes” is contained in a “41” record, however, they are not in the required arrangement for NABOOK to process them correctly. The following example is a valid NABOOK format:

410003+00000001 42....+00061803 43....+00000011 44....+00003003 45....+00000001410004+00000002 42....+00092247 43....+00000016 44....+00026487 45....+00026901410005+00000011 42....+00000835 43....+00000001 44....+00000070

What is shown here are “41” records for Codes 1, 2, and 11. These codes should follow line 1 (410002+?......1)as described above, and should precede the observations in the raw data file. In line 2 you see the date (June 18 2003), the observer code (11 – each different observer gets his/her own number), the instrument type (called 3003 here, although it was actually a DNA03) and a code indicating that the temperature measurements were made using the Fahrenheit scale. The third line refers to the instrument serial number, collimation error and rod serial numbers and the fourth line to the start time, rod on mark and temperature. This information should be entered by the instrument person as the leveling is being run and must be arranged in this order. If not, it will be necessary to edit the data file (refer to NABOOK documentation for detailed explanation of codes and formats).

During leveling an additional possible problem has to do with the NABOOK procedure of requiring no earth-curvature correction and using “standard” accuracies instead of “enhanced” accuracies. This number should be “0” (no curvature correction used and no


enhanced accuracy) in all level runs and is set in the configuration menu in the level. You can tell whether or not the no-curvature correction was used by looking at each rod reading (refer to Leica instrument manual). Here’s an example:

110006+00000014 32..00+00029980 331168+00082104 52..08+0003+009 110007+00000379 32..00+00029660 332168+00163394 52..08+0003+006

The red numbers (6) in Position 5 above indicate that the reading was measured without the earth-curvature correction, but with enhanced accuracy. This particular digit should be 0. Consistency in field procedures should be foremost in these projects. One of the submitted projects used varying choices in different segments of the project, e.i., in one case both the curvature correction and enhanced accuracy were chosen, in some cases only one of the two and in some cases neither. (The digit in the 6th place (8) indicates that the reading itself is made to the .01 millimeter precision.)

One more requirement for the raw data file (as far as NABOOK is concerned) is that no record may exceed 80 characters in length. Records exceeding this length will always be empty beyond the 80th character place, and surplus characters may be safely deleted.

If the StarNetPro program was used to quality control the level run, all code 50 lines will need to be removed, and all beginning and ending elevations set to zero, in addition to the items described above that are needed by NABOOK.

Once the raw data file is properly formatted, it is ready to be processed into files needed for the submission process, including preparation of description files.

Basic File Preparation for “Blue Booking”With the raw field file from level that has been properly formatted as above, it is first run through several steps in the NABOOK program and then through several steps in the NGS programs. These steps have been explained in the order they need to happen. Using VTIS, a CGPS site in Long Beach, CA. as an example, the first leveling segment was named L266151. (Before a leveling project is started, a level line number should be assigned from NGS, in this case L26615.) The NGS 1st order benchmark’s used for VTIS were DY1113 and DY2502 and were given point numbers 1113 and 2502; respectively. The number assigned to the VTIS GRM (the elevation that was to be published) was 7013 and was based on a numbering system determined with the whole project (all segments) in mind to avoid duplicate point numbers.

1. NABOOK – install in folder called NABOOK in the C:\programs\vertpgm directorya. Constant. exe - Choice #1 - create Header.blu file – need to know begin and

end dates of leveling, NGS codes for agencies/firms involved in project

*A1*VERTOBS CSRC CALIFORNIA SPATIAL REFERENCE CENTER 20040610*10*L26615 1 2003090320030903MM8.0 22CALA MSPJOHFRA 2 *11*CSRC LEVELING TO 20 SOUTHERN CA CGPS STATIONS *12*CSRC NAVD88 LEVELING TO CGPS SITE VTIS IN LOS ANGELES CO. *15*COLLIMATION CHECK TAKEN DAILY AND STORED INTERNALLY IN THE NA3003 AND *15*USED TO CORRECT EACH ROD READING.


b. Constant.exe - Choice #2 - create NA.do file – need to know time zone, number of instrument men, their instrument height and if temperature sensors were used

*11*CSRC LEVELING TO 20 SOUTHERN CA CGPS STATIONS (title)T (time zone code) 1 (no. of instrument men) 1 MSP 153 (first inst. man, initials, HI)130 (temperature sensor default value) 30 (temperature sensor default value)

c. NABOOK.exe - move L266151.raw level file, header.blu and na.do to same directory with NABOOK.exe and run – creates L266151.blu and L266151.bok; check bok file for errors in level run and fix; refer to NABOOK documentation for error code explanations

d. Copy Header.blu to top of L266151.blu file and save as L266151.txt (this file now has header records and 40 records in it, as shown below)

*A1*VERTOBS CSRC CALIFORNIA SPATIAL REFERENCE CENTER 20040610*10*L26615 1 2003090320030903MM8.0 22CALA MSPJOHFRA 2 *11*CSRC LEVELING TO 20 SOUTHERN CA CGPS STATIONS *12*CSRC NAVD88 LEVELING TO CGPS SITE VTIS IN LOS ANGELES CO. *15*COLLIMATION CHECK TAKEN DAILY AND STORED INTERNALLY IN THE NA3003 AND *15*USED TO CORRECT EACH ROD READING. *40*03090324391716 39622962 39623219 153130 30 -.021T0738 *41*03090311132502T07380805F64.063.012 8 KM0.484MT 1.56716MSP*43*030903111325020738 -1.942*41*03090325027013T08070957F63.070.002 40 KM1.121MT 51.45792MSP*43*030903250270130807 279.394*41*03090370132502T10031124F70.066.012 40 KM1.123MT -51.45764MSP*43*030903701325021003 -283.362

2. WDDPROC – Install all description programs in a directory of C:\programs\vertpgm or they will not run correctly. You also need to set a path and environment variable to this directory as explained in the NABOOK documentation. When running these programs all needed data files, etc. have to also be in this directory. Because VFPROC installs all programs (*.exe) and all related program files in this directory, it is confusing because the programs are mixed in among the documentation files, program files, etc. For ease of use, rename them as follows (this is also the order that you run the files through them). This puts them at the front (top) of the folder when you open it. Each time you run a set of files through the process, you will need to move all the required files to this directory to run them through the complete process. You can them move them back to a project directory, for this example, L26615_1_VTIS.

1_WDs2d.exe – need to run this on each BM used; go to web, save NGS datasheet as *.txt file (e.i. DY1113.txt file); run 1_WDs2d - changes DY1113.txt to DY1113.dsc file; repeat for all published marks; e.i. DY1113.dsc; DY2502.dsc; VTIS.dsc


2_WExtract.exe – run this program on all *.dsc files created above; name with the same name but with *_mrg.dsc as the name; e.i. DY1113_mrg.dsc; DY2502_mrg.dsc

3_WMrgdesc.exe – run this to merge the existing dsc files into one. May have to run twice or more if you need to merge several files; e.i.:

3_WMrgdesc.exe = first : DY1113_mrg.dsc + DY2502_mrg.dsc = tempmrg.dsc3_WMrgdesc.exe = second: tempmrg.dsc + VTIS_mrg.dsc = L266151.dsc – which now contains all three descriptions

4_WDesc.exe – open the L266151.dsc file; go to Project; fill in all blanks and save. (Project title should be the same as the title submitted to NGS when requesting level line number.) If any descriptions need updating, select it and go to Description and select Edit Description. Edit as needed and save. To add new descriptions for those marks not previously described, go to Description and select New Description. Edit as needed and save. Repeat as necessary. When done adding descriptions, go to File, Exit, and save changes. Make copy of this L266151.dsc and put in project directory for safe keeping.

Note: Party chiefs should have an example of this description file with them, with the NGS description notes so they can properly describe or at least record the needed information. It is difficult to prepare these descriptions when you haven’t been there.

5_WChkdesc.exe – run this on L266151.dsc. View L266151.msg file with Wordpad to see what errors exist in dsc file. Go back to 4_WDesc.exe and edit/fix errors and redo these steps until all errors removed.

6_WPrtdesc.exe – run this on L266151.dsc and view L266151.prn with Wordpad for final description text.

7_WinMakefile.exe – run this on L266151.txt to create the L266151.hgz file

8_WinNewabs.exe – run this program on the L266151.hgz and L266151.dsc. Need to know beginning and ending benchmark and beginning benchmark elevation. This puts the 30 records into the *.hgz file. This creates L266151.abs, an ASCII file to view final results and check for errors

9_Win Readfile.exe – run this on L266151.hgz to get an ASCII file L266151.lst to view final hgz file. Elevations should match preliminary elevations within the misclosure of the level run (these values are not constrained to the ending benchmark at this point in the process).

Addendum to Appendix E

After first submittal to NGS, several items from the above process were slightly revised to accommodate the submittal of the manual measurements into the NGS database and processing software.


First, NGS requested that all *.dsc files (20 in all; one for each CGPS site) be merged into one file for the whole project. This was accomplished by running 3_WMrgdesc.exe on all 20 files to create one project dsc file, L26615.dsc.

Second, NGS requested that a separate ID be given to each possible position of elevation on the CGPS site, the ARD, the GRM and the BPA. This required that additional descriptions for the ARD and BPA be added to the L26615.dsc file (the original idea was to just publish a height on the GRM of each CGPS site). To avoid confusion and possible duplication of point numbers, each ARD was assigned the same point number as the GRM, but with an increase of 200 and each BPA was given an increase of 100 over the GRM. For example, the GRM for VTIS was previously assigned number 7013, so the ARD was assigned 7213 and the BPA was assigned 7113. This convention was held for all 20 sites. The new descriptions were created in 4_WDesc.exe by selecting the dsc file for the GRM and creating a copy to edit for the ARD and then repeating the process for the BPA.

NGS also wanted to better account for the manual measurements to the GRM and BPA from the ARD (which was the only position established by leveling). They created a new “instrument” code to be added to the inst.dat file which is used to create the *.hgz file for processing the level run. The following example shows the inst.dat file used to process the CGPS site level files. It includes a line for the NA3003 (in this example) and one for the steel rule used for the manual measurements:

000010*20*24391716 LEICA NA3003 JOHFRA 000000100000020*20*200RULE1 UNSPECIFIED STEEL/MM-CF JOHFRA 030000000

After this process was completed, NGS had us add extra *15 record lines to the L266151.txt files to explain the manual measurements for each site and some additional *40 record lines that utilized the new *20 record for the steel rule. The following example shows the edited L266151.txt file for VTIS incorporating these additional records (additional data lines highlighted in red):

*A1*VERTOBS CSRC CALIFORNIA SPATIAL REFERENCE CENTER 20040610 *10*L26615 1 2003090320030903MM8.0 22CALA MSPJOHFRA 2 *11*CSRC LEVELING TO 20 SOUTHERN CA CGPS STATIONS *12*CSRC NAVD88 LEVELING TO CGPS SITE VTIS IN LOS ANGELES CO. *15*COLLIMATION CHECK TAKEN DAILY AND STORED INTERNALLY IN THE NA3003 AND *15*USED TO CORRECT EACH ROD READING. *15*THE FIELD HEIGHT DIFFERENCE FOR THE SECTION BETWEEN SSNS 7213 AND 7113 *15*WAS COMPUTED AS FOLLOWS-- *15* +0.2637 METER *15*= 0.2326 METER (MANUAL STEEL RULE MEASUREMENT FROM LEVELED ANTENNA *15* REFERENCE DIVOT (ARD) UP TO BOTTOM OF ADAPTOR (BOA)) *15*+ 0.0311 METER (MANUAL STEEL RULE MEASUREMENT FROM BOA UP TO BASE OF *15* PREAMP (BPA) = MEAN ADAPTOR HEIGHT) *15*THE FIELD HEIGHT DIFFERENCE FOR THE SECTION BETWEEN SSNS 7213(ARD)AND *15*7013(GRM) WAS COMPUTED AS FOLLOWS-- *15* +0.2554 METER *15*= 0.2326 METER (MANUAL STEEL RULE MEASUREMENT FROM LEVELED ANTENNA *15* REFERENCE DIVOT (ARD) UP TO BOTTOM OF ADAPTOR (BOA)) *15*+ 0.0311 METER (MANUAL STEEL RULE MEASUREMENT FROM BOA UP TO BASE OF *15* PREAMP (BPA) = MEAN ADAPTOR HEIGHT) *15*- 0.0083 METER (FROM BPA DOWN TO GEODETIC REFERENCE MARK (GRM),


*15* CONSTANT BASED ON MACHINING SPECIFICATIONS OF *15* ADAPTOR). *40*03090324391716 39622962 39623219 153130 30 -.021T0738 *41*03090311132502T07380805F64.063.012 8 KM0.484MT 1.56716MSP *43*030903111325020738 -1.942 *41*03090325027013T08070957F63.070.002 40 KM1.121MT 51.45792MSP *43*030903250270130807 279.394 *41*03090370132502T10031124F70.066.012 40 KM1.123MT -51.45764MSP *43*030903701325021003 -283.362 *40*030903200RULE1 300RULE1 300RULE1 30 T1830 *41*03090372137113T1830 F64.064.002 1 MT0.001MT0.2637 MSP *43*030903721371131830 *40*030903200RULE1 300RULE1 300RULE1 30 T1840 *41*03090372137013T1840 F64.064.002 1 MT0.001MT0.2554 MSP *43*030903721370131840 The *15, 40, 41 and 43 records are edited to reflect the correct manual measurements and other site related data (point number, date, time, etc.).

After these files are prepared correctly, the L266151.txt file is run through steps 7_WinMakefile.exe, 8_WinNewabs.exe and 9_Win Readfile.exe to create the hgz file, abs file and lst file for submittal to NGS.

This process was run on all stations and resubmitted to NGS. In the future, these steps will be incorporated into the initial process for any level runs to CGPS sites that utilize manual measurements as performed for this project and delineated in this document.


Appendix F - Leveling Input For NA3003

(as required for NGS Vertical Project Submission using Charles Whalen NABook program)

Leica/Wild NAXXXX data recording code blocks for recording single-run, BF leveling to be processed with Whalen's NABOOK program.

Do a collimation check at start of day & set the instrument to apply it. If error exceeds 10.0 (1st & 2nd Order) or 20.0 (3rd order) adjust instrument & reobserve collimation check.

Code 1 - Beginning of day or change in observer/instrument/rods/or a new collimation check1) Date (MMDDYY)2) Observer's code number (1, 2, or 3, etc.)3) Instrument type number (like 2000, 2002, 3000, 3003, etc.)4) Temperature code ( 0 for C or 1 for F)

Code 2 - Equipment used1) Instrument serial number (like 90810)2) Collimation error in seconds of arc (no decimal, like -58 for -5.8")3) Rod 1 serial number (like 25458)4) Rod 2 serial number (like 25534)

Code 11 - Start of leveling section (Set point number to 1)1) Time (HHMM, 24 hour local)2) Rod on mark (1 or 2)3) Temperature (no decimal, key 75 for 75.0 degrees, omit if recording temperatures for gradient)

(Record SPSN as point number for first backsight of each section.)

Code 22 - Reject previous backsight and foresight (No data entries)

Code 33 - Temperature (End of each setup if recording two temperatures for gradient, else omit.)1) Lower probe (no decimal, key 761 for 76.1 degrees)2) Upper probe (no decimal, key 750 for 75.0 degrees)

(Record SPSN as point number for last foresight of each section.)

Code 99 - End of section1) Time (HHMM, 24 hour local)2) Rod on mark (1 or 2)3) Temperature (no decimal, key 75 for 75.0 degrees, omit if recording temperatures for gradient)4) wind & sun codes, like 21

Code 11 for next section, etc. as above

Code 9999 - End of day or change of instrument/rod/observer/or a new collimation check (no data entries)


WIND CODE:0 IF WIND SPEED AVERAGED LESS THAN 10 KM/HR (6 MILES/HOUR)1 IF WIND SPEED AVERAGED 10 TO 25 KM/HR (6 TO 15 MILES/HOUR)2 IF WIND SPEED AVERAGED GREATER THAN 25 KM/HR (15 MILES/HOUR)

SUN CODE:0 IF LESS THAN 25 PERCENT OF THE SETUPS ARE PERFORMED IN SUNNY CONDITIONS.1 IF 25 TO 75 PERCENT OF THE SETUPS ARE PERFORMED IN SUNNY CONDITIONS.2 IF MORE THAN 75 PERCENT OF THE SETUPS ARE PERFORMED IN SUNNY CONDITIONS.

EXAMPLES:

FILE BEGINNING – Code 1 entries (line 1), Code 2 entries (line 2), Code 11 entries (line 3), Start leveling (line 4), First SPSN (line 5):

410001+00000001 42....+00091003 43....+00000001 44....+00003003 45....+00000001 410002+00000002 42....+00091716 43....-00000041 44....+00022962 45....+00023219 410003+00000011 42....+00000757 43....+00000001 44....+00000067 410004+?......1 110005+00005358 83..16+00000000 110007+00005358 32..00+00012170 331108+00103703 52..08+0004+008 110008+00000001 32..00+00011480 332108+00193097 52..08+0004+001 110009+00000001 573..0+00000690 574..0+00023650 83..06-00008939 (etc.)

END OF SECTION – Last SPSN (line 83), Code 99 entries (line 86):

110080+00000025 32..00+00014700 332108+00079758 52..08+0004+004 110081+00000025 573..0+00001140 574..0+00865780 83..06-00054353 110082+00000025 32..00+00008570 331108+00150189 52..08+0003+001 110083+00006353 32..00+00009990 332108+00154331 52..08+0004+004 110084+00006353 573..0-00000280 574..0+00884330 83..06-00054767 410086+00000099 42....+00000915 43....+00000001 44....+00000071 45....+00000002

BEGINNING OF NEXT SECTION – Code 11 (line 87), First SPSN (line 89):

410087+00000011 42....+00000918 43....+00000001 44....+00000072 410088+?......1 110089+00006353 83..16+00000000 110090+00006353 32..00+00009970 331108+00156770 52..08+0004+003 110091+00000001 32..00+00008630 332108+00152634 52..08+0004+005 110092+00000001 573..0+00001340 574..0+00018600 83..06+00000414 110093+00000001 32..00+00013780 331108+00083593 52..08+0003+004

END OF FILE - Last SPSN (line 549), Code 99 entries (line 552), Code 9999 (line 553):

110547+00000043 573..0-00002390 574..0+00889400 83..06-00641862 110548+00000043 32..00+00018370 331108+00108149 52..08+0003+003 110549+00000353 32..00+00017020 332108+00151071 52..08+0003+008 110550+00000353 573..0-00001050 574..0+00924790 83..06-00646155 410552+00000099 42....+00001725 43....+00000001 44....+00000077 45....+00000002 410553+00009999

Refer to manufacturer equipment documentation for explanation of proprietary data lines. Refer to documentation for NABook program for more detailed explanation of codes and formats.


Appendix G - NGS Procedures For Using Leica DNA03 Level (dated 04/09/04)

FIRST: Collimation test - Do first each day or at the beginning of a new project.

Press the “PROG” key, and then from the “PROGRAMS” screen select “3 CHECK & ADJUST”:

From the “CHECK & ADJUST” screen, select “1 SET JOB” From the “SELECT JOB” screen select <NEW>

o Enter values in the “NEW JOB” SCREEN: (normally there will be one job file for each day, if a new project is started later in the day a second C-test will be taken and job file is created)

Job: sasmmddA (initials of observer, month, day, A……..B, C, D)Oper: sas (initials of observer)Cmtl: blankCmt2: blank Then press <SET>

From the “CHECK & ADJUST” screen select “2 SET METHOD”:o Enter values in the “SELECT METHOD” screen:

Method: Always select A X BXStf1: blankStf2: blank Then press <SET>

From the “CHECK & ADJUST” screen, select “3 START”, Follow prompts from screen. Then press <SET>

SECOND: Start the leveling program

From the “PROGRAMS” SCREEN, select “2 LINE LEVELING” From the “LINE LEVELING” screen select “2 SET LINE” From the “NEW LINE” screen enter the following: (A new line name will be

created for every section).

Name: 00010002 (From SPSN # to SPSN #)Meth: BF (Always BF, backsight-foresight)PtID: 0001 (From SPSN #)HO: blankStf1: blankStf2: blankThen press <SET>

From the “LINE LEVELING” screen select “3 SET Tolerances”View the “SET TOLERANCES” screen; Then if correct press <SET>

From the “LINE LEVELING” screen select “4 START”


o On the last set-up, key in the ending SPSN # of the mark leveled to in the comments part of the data screen.

o At this point the leveling screen will be displayed. Anytime while in the leveling routine one can enter a code block into the job data file by pressing the “SHIFT” key then the “PROG” key. The code screen will be displayed and the codes will be entered as follows:

Code 1 Will be entered at the beginning of the day, change in observer, or change in instrument

Code 2 Will be inserted at the beginning of the day or change in level or rodsCode 11 Will be inserted at the beginning of a sectionCode 22 Will reject the previous back-sight and fore-sightCode 33 The temperature code will be inserted after each set-upCode 99 Will be inserted at the end of a sectionCode 9999 Will be inserted at the end of day

LEVEL CODES

Codes are entered by pressing the shift key, and then press the user key to bring up the function menu. Select the code function. Enter the code number and the appropriate information for the code. Once finished, select REC and press the enter key to record the data.

CODE 1 Beginning of Day or Change in Observer/Instrument Type Info 1 ______________Date (MMDDYY) Info 2 ______________Observer’s code number (1, 2, 3, etc) Info 3 ______________Instrument type number (2000, 2002, 3000, 3003, DNA03,etc) Info 4 ______________Temperature code (0 for C or 1 for F)

CODE 2 Equipment Used Info 1 _______________Instrument serial number (like 90810) Info 2 _______________C test error in seconds of arc (no decimal, like –58 for –5.8) Info 3 _______________Rod 1 serial number (like 25458) Info 4 _______________Rod 2 serial number (like 25534)

CODE 11 Start of Leveling Section Info 1 _______________Time (HHMM, 24 hour local) Info 2 _______________Rod on mark (1 or 2) Info 3 _______________Temp (no decimal, key 750 for 75.0 – leave blank if a thermister is used) Info 4 _______________No entry

CODE 22 Reject Previous Back-sight and Fore-sight Info 1 – No entry Info 2 – No entry Info 3 – No entry


Info 4 – No entry

CODE 33 Temperature Gradient Info 1 _______________Lower Probe (no decimal, key 761 for 76.1) Info 2 _______________Upper Probe (no decimal, key 761 for 76.1) Info 3 No entry Info 4 No entry

CODE 99 End of Section Info 1 ______________Date (MMDDYY) Info 2 ______________Observer’s code number (1, 2, 3, etc) Info 3 ______________Temp if thermister not used (756 for 75.6, leave blank if a thermister is used) Info 4 ______________Wind & Sun code

Wind Code:0 - if wind speed averaged less than 6 mph1 - If wind speed averaged 6 to 15 mph2 - If wind speed average averaged greater than 15 mph

Sun Code:0 - if less than 25% of setups are performed in sunny conditions1 - If 25 t0 75% of setups are performed in sunny conditions2 - If more than75 % of setups are performed in sunny conditions

CODE 9999 End of Day or Change of Observer Info 1 ______________ Leave blank Info 2 ______________ Leave blank Info 3 ______________ Leave blank Info 4 ______________ Leave blank

DNA03 LEVEL SETTINGS

The following settings can be set from the “Meas & Rec” screen. This screen comes up when the level is first turned on. If the level is in the “PROGRAM” mode, exit the program to see the “Meas & Rec” screen.

SET MEASUREMENT MODE

From the “Meas & Rec” screen, press the MODE key. From the “MEASURE MODE” screen, set the following to:

Mode: Mean sN: blankN Min: 3


N Max: 10SdevM / 20m: 0.00002

Highlight < SET > then press the red key.

SET CURVATURE CORRECTION OFF

From the “Meas & Rec” screen: Press the SHIFT PROGRAM keys. From the “MENU” screen, select “ 2 ALL SETTING” then press the red key. From the “ALL SETTINGS” screen, select “ 2 MEASURING” then press the red

key. From the “MEASURING SETTINGS” screen, set the following:

Codeset: BeforeDecimals: 0.00001GSI-Format: GSI – 8EarthCurv: No

Highlight < SET > , then press the red key

SET UNITS

From the “Meas & Rec” screen: Press the SHIFT PROGRAM keys. From the “MENU” screen, select “2 ALL SETTING” then press the red key. From the “ ALL SETTING”screen, select “ 4 UNITS” then press the red key. Set to “Metre”, then select < SET >, then press the red key.

SET DATE AND TIME

From the “Meas & Rec” screen: Press the SHIFT PROGRAM keys. From the “MENU” screen, select “ 2 ALL SETTING” then press the red key. From the “ ALL SETTING”screen, select “ 5 DATE/TIME” then press the red

key.Set the date and time. Then select < SET >, then press the red key.

SET INCREMENT MODE

From the “Meas & Rec” screen: Press the SHIFT USER keys. From the “FUNCTIONS” screen , select “4 PtID & Increment”

Set the following:PTID: 1INCR: 1

Select < SET > then press the red key.


differential leveling to cgps stations

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