u.s. coast & geodetic survey/noaa steps to creating a nautical chart
DESCRIPTION
U.S. Coast & Geodetic Survey/NOAA Steps to Creating a Nautical Chart. Historic types of surveys required Astronomical Observations Land survey (triangulation) Tide Gauges Shoreline Mapping Hydrography. - PowerPoint PPT PresentationTRANSCRIPT
U.S. Coast & Geodetic Survey/NOAASteps to Creating a Nautical Chart
Historic types of surveys required – Astronomical Observations– Land survey (triangulation)– Tide Gauges– Shoreline Mapping– Hydrography
Theodolite instrument for precise astronomical observations to determine latitude, longitude, and azimuth
Astronomical observations were necessary to determine the position and orientation of selected points in a survey network.
View through Telescope at desired star
Star aligned with cross-hair
Astromical Observations performed at this site to determine initial latitude, longitude, and azimuth.
Survey Network
TRIANGULATION
• Baselines (BL) 1 & 2 are measured
•All angles of the triangles are measured
•Sides of all triangles are computed
• Computed length BL2 is compared to measured length of BL2
ME
AS
UR
ED
BA
SE
LIN
E 1
Angle measured
Angle measured
Angle measured
Angle measured
ME
AS
UR
ED
BA
SE
LIN
E 2
= survey mark
STEPS
TIDE
GAUGES
• Tide zone boundaries shown in red and orange
• Within each zone tidal height and time correctors are equal
•Tidal data required to correct depths and to determine horizontal position of shoreline
=Tide gauge
4. Plane table moved to another location and procedure repeated
5. Points of intersection define position of distant objects
6. Shoreline is drawn through intersecting points; also range & bearing determine positions
1. Plane table is set-up over known point
2. Paper map correctly oriented
3. Distant objects sighted upon and lines drawn from present position toward distant objects
PLANE TABLE MAPPING
6 7.2
9.1
6.5
6.1
5.1
7
8.9
7.87 8
7.9
9.397
5
6
9.285.5
7.1
Depths (soundings) are measured continuously along dotted lines. Sextant angle fixes are taken at locations indicated by green bars.
9.59.4
5.7
8
5.2
8.59.2
9.5
9.1
8.8
8.5
8.3
87.9
7.6
7.2
7.2
HYDROGRAPHY
• Two sextant angles at periodic points along the launch’s path determine position of the launch
= survey mark
GEODETIC SURVEYSHORELINE SURVEYTIDAL SURVEY
= tide gauge
HYDROGRAPHIC FIELD SHEET