department of electrical and computer engineering electroscience laboratory the ohio state...
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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.