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SMAP- SMAP- JPL/Caltech proprietary. Not for public release or redistribution. For planning and discussion purposes only. National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Pasadena, California National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Pasadena, California Radio Frequency Interference Mitigation for the Planned SMAP Radar and Radiometer Michael Spencer, Samuel Chan , Eric Belz Jet Propulsion Laboratory, California Institute of Technology Jeffrey Piepmeier, Priscilla Mohammed, Edward Kim NASA’s Goddard Space Flight Center Joel T. Johnson The Ohio State University
Emitters appear to be “stationary” in frequency, geographic position.
Ground-commandable, tunable carrier frequency to hop frequencies and avoid PARTICULARLY BAD spectral areas.
RFI which is still encountered (estimated to be approximately 10% of time) will be filtered in ground processing.
Other design consideration is that receiver should not compress/saturate for strong out-of-band sources.
Requirement/Allocation: RFI shall not contribute more than 0.4 dB 1-sigma to the backscatter measurement. Up to 2% of the data can is allowed to be flagged “ bad data ” where RFI is too excessive to mitigate. HH HV noise RF Bandwidth (100 MHz acceptance) IF, Digital System Bandwidth, 5 MHz 1 MHz
Simulation of RFI environment using characteristics of known emitters and SMAP instrument parameters.
Advantages: Utilizes SMAP antenna pattern and scan characteristics. Capable of simulating known future systems.
Disadvantages: Only complete data set of emitters available to us (thus far) is over North America. Difficult to obtain all necessary parameters of interfering radars.
Key results to date:
Simulation predicts probability of exceeding threshold for 0.4 dB interference (-110 dBm average power in any given range line) at 10% over N. America in any given 1 MHz band.
Simulation predicts probability of exceeding power level sufficient to compress front end < 0.1 %.
Simulation predicts probability of range line having at least one pulsed event exceeding power level to compress IF < 1%.
Simulation predicts generally lower probability of interference in lower part of allocation < 1260 MHz, as opposed to upper part of allocation > 1260 MHz
Assessment of Ground Emitters Using Current L-Band Data Sets
Analysis of JAXA ALOS/PALSAR data.
Advantages: Utilizes real data in band of interest. Data set has measurements from all over the globe.
Disadvantages: Antenna pattern and data collection technique very different from SMAP. PALSAR only covers 32 MHz of 85 MHz allocation. Data only valid for current RFI environment, not future.
Key results to date:
Survey of PALSAR data shows primarily pulsed emitters typical of air surveillance radars (87% of occurrences) with another 13% of occurrences miscellaneous (including CW) sources, with high concentration over urban areas.
Quantitative survey of pulsed emitters over North America indicate probability of having more than 5 SMAP range lines (out of 112) contaminated by RFI is < 1 % for any randomly chosen 1 MHz band.
Analysis of impulse response function suggests that approximately 15 range lines (out of 112) could be excised and the measurement would still meet the 0.4 dB requirement. The analysis suggests 15 contaminated range lines is a very low probability event.
Experiments to “clean up” PALSAR data using detection and filtering scheme have thus far been very successful, with residual errors < 0.1 dB.