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Chan, Samuel

Publications and source records attributed to Chan, Samuel.

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Radio Frequency Interference Mitigation for the Planned SMAP Radar and Radiometer

NASA's planned SMAP mission will utilize a radar operating in a band centered on 1.26 GHz and a co-observing radiometer operating at 1.41 GHz to measure surface soil moisture. Both the radar and radiometer sub-systems are susceptible to radio frequency interference (RFI). Any significant impact of such interference requires mitigation in order to avoid degradation in the SMAP science products. Studies of RFT detection and mitigation methods for both the radar and radiometer are continuing in order to assess the risk to mission products and to refine the performance achieved.

radiometer↗
NASA NTRS2011

RFI Mitigation and Detection for the SMAP Radar

The planned Soil Moisture Active Passive (SMAP) mission will use both active radar and passive radiometer instruments at L-Band to measure and monitor both soilmoisture and freeze/thaw state globally. The frequency band allocated for the SMAP radar is shared with the Global Navigation Satellite Systems and ground-basedradiolocation services. Signals from those users present significant sources of anthropogenic radio frequency interference (RFI) which contaminate the radarmeasurements. To mitigate RFI, the radar is designed with tunable operating frequency, which allows the center frequency to be tuned to avoid RFI. The filtering scheme in the receiver is configured to get a high level of RFI suppression. To meet the high accuracy measurement requirements, RFI detection and correction will be required during ground data processing. Some candidate algorithms have been evaluated, and they have been tested against simulated SMAP data derived from the PALSAR data.

Soil Moisture Active Passive (SMAP)↗
NASA NTRS2011

The Planned Soil Moisture Active Passive (SMAP) Mission L-Band Radar/Radiometer Instrument

The Soil Moisture Active/Passive (SMAP) mission is a NASA mission identified by the NRC 'decadal survey' to measure both soil moisture and freeze/thaw state from space. The mission will use both active radar and passive radiometer instruments at L-Band. In order to achieve a wide swath at sufficiently high resolution for both active and passive channels, an instrument architecture that uses a large rotating reflector is employed. The instrument system has completed the preliminary design review (PDR) stage, and detailed instrument design has begun. In addition to providing an overview of the instrument design, two recent design modifications are discussed: 1) The addition of active thermal control to the instrument spun side to provide a more stable, settable thermal environment for the radiometer electronics, and 2) A 'sequential transmit' strategy for the two radar polarization channels which allows a single high-power amplifier to be used.

radiometer↗
NASA NTRS2009

RFI Study for the SMAP Radar

The Soil Moisture Active/Passive (SMAP) mission has the scientific objective of measuring both soil moisture and freeze/thaw state from space. The mission will make both active radar and passive radiometer measurements at L-Band in order to retrieve soil moisture. Some studies, how-ever, indicated that these measurements are susceptible to radio frequency interference (RFI) in several geographic locations. As SMAP is a global mission and its mission life is 3 years, it is crucial for SMAP to understand the RFI over the whole globe and its temporal behavior. There will be impacts to the instrument system design and ground data processing in order to mitigate RFI. In this paper, strategies and procedures for performing this RFI study will be presented, and some results utilizing the RFI observed in the ALOS PALSAR data are described. The nature of the ob-served RFI is characterized and suggests some bands are relative free of RFI. The SMAP radar system will use a 1 MHz bandwidth, which can be placed within these suggested "clear" frequencies. The ALOS PALSAR data covers 28 MHz within the 80 MHz allocated for active L-Band remote sensing. In addition, an initial analysis with UAVSAR data, which uses the entire 80 MHz allocation, indicates the relative severity of RFI over the whole band. An algorithm to remove RFI is suggested and its performance is shown for some data from ALOS PALSAR and UAVSAR.

ALOS PALSAR↗
NASA NTRS2009

The Soil Moisture Active/Passive (SMAP) Mission Radar: A Novel Conically Scanning SAR

The Soil Moisture Active/Passive (SMAP) mission is a NASA mission identified by the NRC "decadal survey" to measure both soil moisture and freeze/thaw state from space. The mission will use both active radar and passive radiometer instruments at L-Band. In order to achieve a wide swath at sufficiently high resolution for both active and passive chan-nels, an instrument architecture that uses a large rotating reflector is employed. The active radar will further utilize SAR processing in order to obtain the sub-footprint resolution necessary for the geophysical retrievals. The SMAP radar has a unique geometry where the antenna footprint is continuously rotated about nadir in a conical fashion, as opposed to the more common side-looking SAR design. In additional to the unconventional scan geometry, the SMAP radar must address the effects of Faraday rotation and radio frequency interference (RFI), both consequences of the L-Band frequency of operation.

L-band↗
NASA NTRS2009

SMAP's Radar OBP Algorithm Development

An approach for algorithm specifications and development is described for SMAP's radar onboard processor with multi-stage demodulation and decimation bandpass digital filter. Point target simulation is used to verify and validate the filter design with the usual radar performance parameters. Preliminary FPGA implementation is also discussed.

soil moisture↗
NASA NTRS2004

Onboard FPGA-based SAR processing for future spaceborne systems

We present a real-time high-performance and fault-tolerant FPGA-based hardware architecture for the processing of synthetic aperture radar (SAR) images in future spaceborne system. In particular, we will discuss the integrated design approach, from top-level algorithm specifications and system requirements, design methodology, functional verification and performance validation, down to hardware design and implementation.

spaceborne systems↗