Studies of Radio Frequency Interference Effects at C-band IGS Quarterly Review Joel T.
Download ReportTranscript Studies of Radio Frequency Interference Effects at C-band IGS Quarterly Review Joel T.
Studies of Radio Frequency Interference Effects at C-band IGS Quarterly Review
Joel T. Johnson Department of Electrical and Computer Engineering ElectroScience Laboratory The Ohio State University 10th November 2005
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
T B [K]:
6.8 GHz H Max over 6 months T [K]: 10.7 GHz |U| Max over 6 months
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
ElectroScience Lab
C-band Channel Frequencies
IPO simulations using databases of registered emitters used to develop current CMIS channel plan Multiple channels used in a cross-freq RFI detection algorithm; discard corrupted channels Multi-channel airborne data available from PSR/C since 1999 High frequency/time resolution data 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 – – 1/04- 12/04: Deployed in SMEX04 and AASI04 exp (125K) 1/05- 12/05: Data analysis, deployed in WB-57F (30K) (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
Advanced Radiometer Receiver
Properties of traditional radiometer: – – very “slow” instrument Pulsed interferer (~ m sec)
power integrated for msec before being digitized
Time Radiometer integration period (~msec) 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)
ElectroScience Lab
Digital Receiver Backend
• • •
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
200 MSPS 10 bit ADC’s Implemented in Altera FPGA’s Real-time “pulse blanking” algorithm 1K FFT = high spectral resolution RFI removal •
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 filtering/ pulse blanking 1K FFT Spectral processing/ integration
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
AASI04 Test Flight
The largest CISR dataset is from a test flight on October 8 th , 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
ElectroScience Lab
Circles in Figure mark WFF and NDBC Buoy
Time
PSR Images: AASI04 Test Flight over Buoy
Time
ElectroScience Lab
Corresponding CISR Data (to 6.1 GHz)
Provides precise knowledge of RFI center frequency Allows possibility of frequency domain blanking to remove RFI Calibrations show frequency domain blanking effective against narrowband 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
ElectroScience Lab
Calibrated CISR data for the point marked with green line shows narrowband RFI in PSR channel 4; calibration shows contribution ~4-5K to PSR
Use of Asynchronous Pulse Blanking (APB) at C-band
APB on/off data was recorded by CISR throughout C-band Maximum raw data observed 5.7-5.8 GHz 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
ElectroScience Lab
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 Source Locations near Flight Path Histogram of Source Center Frequencies
PSR Interference Level Statistics
21600 PSR pixels in more rural Texas: 18:08-18:23 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
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 % 12.5
30.8
30.6
44.1
1 Channel % 2 Channel % 3 ChanneI % Algorithm failed % 13.0
19.3
27.0
1.3
11.4
3.0
18.8
19.7
27.0
27.0
1.3
1.3
0.6
5.9
27.0
1.3
1 Channel % 2 Channel % 3 ChanneI % Algorithm failed % 10.7
22.6
53.1
1.1
3.6
11.5
1.1
1.5
13.8
1.7
53.1
53.1
1.1
0.1
53.1
1.1
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.