Department of Electrical and Computer Engineering ElectroScience Laboratory The 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 l Both C- and X-bands have no significant protected spectrum for radiometry l Data from both AMSR-E and WindSat radiometers show RFI problems l Increasing transmissions in these bands compromise EDR retrievals, esp. soil moisture and sea surface temperature l 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 months 6.8 GHz H Max over 6 months T B [K]: T [K]:

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 l GOAL 1: Acquire airborne high resolution data to improve knowledge of C-band RFI environment and to validate and enhance CMIS RFI forecasts l GOAL 2: Demonstrate improvements in RFI mitigation that can be obtained through advanced receiver technologies l 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 l NOAA/ETL and OSU hardware leveraged off of other system development projects (a NASA IIP for OSU); only minimal hardware support from IPO l OSU backend is a FPGA based-digital receiver; can configure into several observational modes

Outline l Administrative Information l Advanced Radiometer Receiver l Summary of Accomplishments l Current Efforts and Future Plans

Administrative Information l 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) l Who is involved: – Johnson + students/staff (Ohio State) – Steve Ellingson + students/staff (Virginia Tech) – Al Gasiewski + staff (NOAA/ETL) (under other IPO support) l Funding Status: – Funded through end of project (12/31/05) – Developing proposal for continued RFI studies

ElectroScience Lab Advanced Radiometer Receiver l Properties of traditional radiometer: –very “slow” instrument l power integrated for msec before being digitized –a single, large bandwidth channel l susceptible to narrow band interference l Our design uses a digital receiver for rapid sampling –can mitigate temporally localized RFI in real time l Our design samples 100 MHz, and performs a 1024 point FFT –can mitigate spectrally localized RFI, tuned throughout C-band l Processor operates in real time to reduce final data rate –implemented in hardware (FPGA’s) l 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; MHz channels from GHz Can compare data against simultaneous PSR analog sub- channels; assess PSR 4-channel RFI algorithm Digital Receiver Backend 200 MSPS 10 bit ADC’s Digital filtering/ pulse blanking 1K FFT Spectral processing/ integration Implemented in Altera FPGA’s Real-time “pulse blanking” algorithm 1K FFT = high spectral resolution RFI removal

Summary of Accomplishments l 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 l Detailed analysis of AASI04 data provides info on RFI source properties + assessment of 4 sub-band mitigation algorithm l Examples obtained to illustrate advantages of digital receiver l RFI analysis of WindSat data performed in support of these efforts l Matchups of AASI04/WB-57 RFI with source database in progress

ElectroScience Lab AASI04 Test Flight l The largest CISR dataset is from a test flight on October 8 th, 2004 in preparation for the AASI04 campaign l Note PSR includes 4 analog C-band channels for RFI mitigation ( , , , GHz) l Comparison of PSR/ CISR data enables test of digital vs. analog methods l 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

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 Calibrated CISR data for the point marked with green line shows narrowband RFI in PSR channel 4; calibration shows contribution ~4-5K to PSR

ElectroScience Lab Use of Asynchronous Pulse Blanking (APB) at C-band l APB on/off data was recorded by CISR throughout C-band l Results >5.8 GHz show no influence of blanker l Results < 5.8 GHz show strong influence of blanker l As expected from freq. allocations in US Maximum raw data observed GHz

WB-57F Deployment l Test flight over Texas cities, 8/25/05 l PSR/C, CISR, and CADD sensors l Datasets can be intercompared to assess performance l CISR provides highest spectral resolution l 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 l IPO has made JSC unclassified source database available, contains data from GHz, GHz l Database includes power, antenna, and sometime pol info Histogram of Source Center FrequenciesSource Locations near Flight Path

PSR Interference Level Statistics PSR freq (GHz) Clean % Channel % Channel % ChanneI % 53.1 Algorithm failed % PSR pixels near DFW: 17:54-18:08 UTC PSR freq (GHz) Clean % Channel % Channel % ChanneI % 27.0 Algorithm failed % PSR pixels in more rural Texas: 18:08-18:23 UTC

Current Efforts and Future Plans l Will continue analysis of datasets until project end at 12/31/05 l Database matchups will test methods for forecasting received brightness from database information l 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 l X-band RFI also needs examination: PSR has 4 sub-bands, AMSR/E and WindSat show problems outside US

Summary l Project has provided a set of high time and frequency resolution airborne data to improve knowledge of C-band RFI environment l Project has provided qualitative evidence of potential failure modes for four channel RFI mitigation algorithms l Project has demonstrated that advanced receiver technologies can improve RFI mitigation l Analysis of data continuing, including assessment of forecasts based on source database information l Currently proposing continued studies to the IPO in collaboration with NOAA/ETL, Virginia Tech, University of Michigan, and NASA GSFC

Project Publications l J. T. Johnson, A. J. Gasiewski, et al, “Airborne radio frequency interference studies at C-band using a digital receiver,'' submitted to IEEE TGRS, l 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. l J. T. Johnson, A. J. Gasiewski, et al, “Airborne radio frequency interference studies at C-band using a digital receiver,'' IGARSS’04. l 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, l 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.