Department of Electrical and Computer EngineeringElectroScience LaboratoryThe Ohio State University

10th November 2005

Studies of Radio Frequency Interference Effects at C-band

IGS Quarterly Review

Joel T. Johnson

ElectroScience Lab

C- and X-band RFI in WindSat Data

Both C- and X-bands have no significant protected spectrum for radiometry

Data from both AMSR-E and WindSat radiometers show RFI problems

Increasing transmissions in these bands compromise EDR retrievals, esp. soil moisture and sea surface temperature

IPO/CMIS contractor have proposed a multi-channel C-band

receiver for CMIS, no modifications for X-band

10.7 GHz |U| Max over 6 months6.8 GHz H Max over 6 months

TB [K]: T [K]:

C-band Channel Frequencies

IPO simulations using databases of registered emitters used to developcurrent CMIS channelplan

Multiple channels used in a cross-freq RFI detection algorithm; discard corrupted channels

Multi-channel airborne data available from PSR/C since1999

High frequency/time resolutiondata obtained from CISR since 2004 under this project

Purpose

GOAL 1: Acquire airborne high resolution data to improve knowledge of C-band RFI environment and to validate and enhance CMIS RFI forecasts

GOAL 2: Demonstrate improvements in RFI mitigation that can be obtained through advanced receiver technologies

Project is a collaboration between OSU, NOAA/ETL, and Virginia Tech:– NOAA/ETL PSR/C provides antenna/front end in airborne campaigns– OSU provides RFI observing and mitigating receiver backend– Virginia Tech assists in data analysis and interpretation

NOAA/ETL and OSU hardware leveraged off of other system development projects (a NASA IIP for OSU); only minimal hardware support from IPO

OSU backend is a FPGA based-digital receiver; can configure into several observational modes

Outline

Administrative Information

Advanced Radiometer Receiver

Summary of Accomplishments

Current Efforts and Future Plans

Administrative Information

Project schedule and budget information:– 8/03- 12/03: Initial system development (30K) – 1/04- 12/04: Deployed in SMEX04 and AASI04 exp (125K) – 1/05- 12/05: Data analysis, deployed in WB-57F (125K)

Who is involved:– Johnson + students/staff (Ohio State)– Steve Ellingson + students/staff (Virginia Tech)– Al Gasiewski + staff (NOAA/ETL) (under other IPO support)

Funding Status: – Funded through end of project (12/31/05)– Developing proposal for continued RFI studies

ElectroScience Lab

Advanced Radiometer Receiver

Properties of traditional radiometer: – very “slow” instrument

power integrated for msec

before being digitized

– a single, large bandwidth channel susceptible to narrow band interference

Our design uses a digital receiver for rapid sampling– can mitigate temporally localized RFI in real time

Our design samples 100 MHz, and performs a 1024 point FFT – can mitigate spectrally localized RFI, tuned throughout C-band

Processor operates in real time to reduce final data rate– implemented in hardware (FPGA’s)

C-Band Interference Suppressing Radiometer (CISR)

Radiometer integration period (~msec)Time

Pulsed interferer (~sec)

• Example data: high spectral resolution

for CW and wideband RFI mitigation

• Numerous sources observed; compare observations to IPO forecasts

• Most sources observed are continuous,

pulsed sources < 5.8 GHz only

• Digital receiver samples 100 MHz and includes pulse blanking and 1024 point FFT processor

• Samples IF from PSR downconverter; 22 100 MHz channels from 5.5-7.7 GHz

• Can compare data against simultaneous PSR analog sub-channels; assess PSR 4-channel RFI algorithm

Digital Receiver Backend

200 MSPS10 bitADC’s

Digital filtering/pulse blanking

1K FFTSpectralprocessing/integration

Implemented inAltera FPGA’s

Real-time“pulse blanking”algorithm

1K FFT = highspectral resolutionRFI removal

Summary of Accomplishments

Datasets obtained from three deployments:– SMEX04 (August, Tuscon, AZ and Northern Mexico, Navy P-3)

• Small dataset recorded, interface and system issues resolved

– AASI04 (October, test flight near Wallops Island, VA, Navy P-3)• Approximately 2 hours of data recorded, numerous RFI sources

– WB-57F test flight (August 05, high altitude flight over Texas cities)• Approximately 2 hours of data recorded, numerous RFI sources

Detailed analysis of AASI04 data provides info on RFI source properties + assessment of 4 sub-band mitigation algorithm

Examples obtained to illustrate advantages of digital receiver

RFI analysis of WindSat data performed in support of these efforts

Matchups of AASI04/WB-57 RFI with source database in progress

ElectroScience Lab

AASI04 Test Flight The largest CISR dataset is from a test flight on October 8th, 2004 in preparation for the

AASI04 campaign

Note PSR includes 4

analog C-band channels

for RFI mitigation

(5.8-6.2, 6.3-6.7,

6.75-7.1, 7.15-7.5 GHz)

Comparison of PSR/

CISR data enables

test of digital vs.

analog methods

Use NOAA/ETL algorithm

for RFI removal in 4 sub-band data

Circles in Figure mark WFF and NDBC Buoy

ElectroScience Lab

PSR Images: AASI04 Test Flight over Buoy

Time

Time

ElectroScience Lab

Corresponding CISR Data (to 6.1 GHz)

Provides preciseknowledge ofRFI centerfrequency

Allows possibilityof frequency domain blankingto remove RFI

Calibrationsshow frequencydomain blankingeffective againstnarrowband RFI

ElectroScience Lab

CISR Advantages over PSR

PSR 4 x400 MHz channels show strong RFI; 4 channel algorithm chooses channel 4 (least corrupted) as correct

Calibrated CISR data forthe point marked with green lineshows narrowband RFI in PSRchannel 4; calibration showscontribution ~4-5K to PSR

ElectroScience Lab

Use of Asynchronous Pulse Blanking (APB) at C-band

APB on/off data was

recorded by CISR

throughout C-band

Results >5.8 GHz show

no influence of blanker

Results < 5.8 GHz show

strong influence of blanker

As expected from freq.

allocations in US

Maximum raw data observed 5.7-5.8 GHz

WB-57F Deployment

Test flight over Texas cities, 8/25/05 PSR/C, CISR, and CADD sensors Datasets can be intercompared to

assess performance CISR provides highest spectral

resolution High altitude (18.9 km) environment

of unpressurized WB-57 payload

bay thermally challenging

NASA WB-57F

Flight Plan

CISR onboard WB-57

Sample WB-57 CISR Data: 17:55-17:59 UTC

Example Matchup Studies

IPO has made JSC unclassified source database available, contains data from 4.9-5.9 GHz, 6.2-7 GHz

Database includes power, antenna, and sometime pol info

Histogram of Source Center FrequenciesSource Locations near Flight Path

PSR Interference Level Statistics

PSR freq

(GHz)

5.8-6.2

6.3-6.7

6.75-7.1

7.15-7.5

Clean % 12.5 30.8 30.6 44.1

1 Channel

%

10.7 3.6 1.5 0.1

2 Channel

%

22.6 11.5 13.8 1.7

3 ChanneI

%

53.1 53.1 53.1 53.1

Algorithm failed %

1.1 1.1 1.1 1.1

21600 PSR pixels near DFW: 17:54-18:08 UTC

PSR freq

(GHz)

5.8-6.2

6.3-6.7

6.75-7.1

7.15-7.5

Clean % 39.6 41.8 49.1 65.2

1 Channel

%

13.0 11.4 3.0 0.6

2 Channel

%

19.3 18.8 19.7 5.9

3 ChanneI

%

27.0 27.0 27.0 27.0

Algorithm failed %

1.3 1.3 1.3 1.3

21600 PSR pixels in more rural Texas: 18:08-18:23 UTC

Current Efforts and Future Plans

Will continue analysis of datasets until project end at 12/31/05

Database matchups will test methods for forecasting received brightness from database information

We believe that sufficient datasets exist at this point to perform a comprehensive review of C-band RFI for CMIS– Utilize satellite, aircraft, and database information in a combined

study– Produce an improved RFI forecasting tool for CMIS– Produce an improved 4 channel mitigation algorithm– Provide recommendations to IPO regarding CMIS freqs– Assess new technologies for future CMIS instruments

X-band RFI also needs examination: PSR has 4 sub-bands, AMSR/E and WindSat show problems outside US

Summary

Project has provided a set of high time and frequency resolution airborne data to improve knowledge of C-band RFI environment

Project has provided qualitative evidence of potential failure modes for four channel RFI mitigation algorithms

Project has demonstrated that advanced receiver technologies can improve RFI mitigation

Analysis of data continuing, including assessment of forecasts based on source database information

Currently proposing continued studies to the IPO in collaboration with NOAA/ETL, Virginia Tech, University of Michigan, and NASA GSFC

Project Publications

J. T. Johnson, A. J. Gasiewski, et al, “Airborne radio frequency interference studies at C-band using a digital receiver,'' submitted to IEEE TGRS, 2005.

S. W. Ellingson and J. T. Johnson, “A polarimetric survey of radio frequency interference in C- and X-bands in the continental United States using WindSat radiometry,'' to appear, IEEE TGRS, WindSat special issue.

J. T. Johnson, A. J. Gasiewski, et al, “Airborne radio frequency interference studies at C-band using a digital receiver,'' IGARSS’04.

S. W. Ellingson and J. T. Johnson, “Measurements of L- and C-Band RFI from Earth observing remote sensing instruments,'‘ Workshop in Mitigation of Radio Frequency Interference in Radio Astronomy, 2004.

J. T. Johnson and S. W. Ellingson, “A polarimetric survey of RFI in C- and X-bands in the continental United States using WindSAT radiometry,” APS/URSI 2005.