Soil Moisture Active/Passive (SMAP) L-Band Microwave Radiometer Post-Launch Calibration Upgrade

Peng, Jinzheng; Misra, Sidharth; Piepmeier, Jeffrey R.; Dinnat, Emmanuel P.; Yueh, Simon; Meißner, Thomas; Vine, David M. Le; Shelton, K.; Freedman, A. P.; Dunbar, R. S.; Chan, S.; Bindlish, Rajat; Amici, Giovanni De; Mohammed, Priscilla N.; Liang, Hong; Hudson, Derek; Jackson, Thomas J.

doi:10.1109/jstars.2019.2902492

Cited by 18 publications

(23 citation statements)

References 15 publications

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“…Far from the −3 dB beamwidth, the SMAP antenna gain decreases rapidly and signals coming further away from the −3 dB beamwidth are expected to be greatly attenuated. As published in [42], the antenna pattern is very symmetric in azimuth within the 3dB antenna beamwidth, consequently we have disregarded azimuthal variations.…”

Section: Smap Antenna Pattern Impactmentioning

confidence: 99%

The Use of SMAP-Reflectometry in Science Applications: Calibration and Capabilities

et al. 2019

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The Soil Moisture Active Passive (SMAP) mission became one of the newest spaceborne Global Navigation Satellite System–Reflectometry (GNSS-R) missions collecting Global Positioning System (GPS) bistatic radar measurements when the band-pass center frequency of its radar receiver was switched to the GPS L2C band. SMAP-Reflectometry (SMAP-R) brings a set of unique capabilities, such as polarimetry and improved spatial resolution, that allow for the exploration of scientific applications that other GNSS-R missions cannot address. In order to leverage SMAP-R for scientific applications, a calibration must be performed to account for the characteristics of the SMAP radar receiver and each GPS transmitter. In this study, we analyze the unique characteristics of SMAP-R, as compared to other GNSS-R missions, and present a calibration method for the SMAP-R signals that enables the standardized use of these signals by the scientific community. There are two key calibration parameters that need to be corrected: The first is the GPS transmitted power and GPS antenna gain at the incidence angle of the measured reflections and the second is the convolution of the SMAP high gain antenna pattern and the glistening zone (Earth surface area from where GPS signals scatter). To account for the GPS transmitter variability, GPS instrument properties—transmitted power and antenna gain—are collocated with information collected from the CYclone Global Navigation Satellite System (CYGNSS) at SMAP’s range of incidence angles (37.3° to 42.7°). To account for the convolutional effect of the SMAP antenna gain, both the scattering area of the reflected GPS signal and the SMAP antenna footprint are mapped on the surface. We account for the size of the scattering area corresponding to each delay and Doppler bin of the SMAP-R measurements based off the SMAP antenna pattern, and normalize according to the size of a measurement representative to one obtained with an omnidirectional antenna. We have validated these calibration methods through an analysis of the coherency of the reflected signal over an extensive area of old sea ice having constant surface characteristics over a period of 3 months. By selecting a vicarious scattering surface with high coherency, we eliminated scene variability and complexity in order to avoid scene dependent aliases in the calibration. The calibration method reduced the dependence on the GPS transmitter power and gain from ~1.08 dB/dB to a residual error of about −0.2 dB/dB. Results also showed that the calibration method eliminates the effect of the high gain antenna filtering effect, thus reducing errors as high as 10 dB on angles furthest from SMAP’s constant 40° incidence angle.

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Section: Smap Antenna Pattern Impactmentioning

confidence: 99%

The Use of SMAP-Reflectometry in Science Applications: Calibration and Capabilities

et al. 2019

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“…In the calibration for data product version 4, the reflector emissivity was calibrated first by three different research teams This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ using different approaches and datasets, and the results agreed within 0.5% for the reflector loss [10]. Then the other calibration parameters (antenna gain, equivalent TB of the noise diode, and the offset to the equivalent TB of the reference load) were concurrently recalibrated (i.e., multiple calibration parameters were calibrated simultaneously).…”

mentioning

confidence: 84%

“…The radiometer L1B data product version 3 was released in April 2016. The performance of version 3 during the first year on orbit is reported in [8], and the post-launch calibration and part of its validation are described in [9]. The reflector emissivities measured before launch were used.…”

mentioning

confidence: 99%

“…Validation results for data product version 3 show that the SMAP TA is 2.6 K warmer than the reference forward model simulation over CS, and that the averaged SMAP TB is 2.6 K colder over land than the averaged SMOS TB (compared at the top of the atmosphere for the two L-band satellites with co-located and concurrent measurements), including the update of the reflector's thermal model. Also, there is downward dip in the calibration over the global ocean during eclipse seasons [9]. In order to remove these biases and mitigate the calibration drift, the SMAP radiometer was re-calibrated, and the corresponding data product, version 4, was released in 2018 [10].…”

mentioning

confidence: 99%

“…Also, there is downward dip in the calibration over the global ocean during eclipse seasons [9]. In order to remove these biases and mitigate the calibration drift, the SMAP radiometer was re-calibrated, and the corresponding data product, version 4, was released in 2018 [10].…”

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confidence: 99%

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Soil Moisture Active/Passive (SMAP) L-Band Microwave Radiometer Post-Launch Calibration Revisit: Approach and Performance

Peng

Misra

Piepmeier

et al. 2021

IEEE J. Sel. Top. Appl. Earth Observations Remote Sensing

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The soil moisture active passive (SMAP) microwave radiometer is a fully-polarimetric L-band radiometer flown on the SMAP satellite in a 6 AM /6 PM sun-synchronous orbit at 685-km altitude. After the SMAP L1B_TB data product version 4 was released in 2018, the radiometer has undergone further calibration and validation. The goal is to reduce the difference between antenna temperature of ascending and descending orbits during the eclipse, and to reduce the dips in the calibration drift over the cold sky (CS) during the eclipse seasons in 2017 and 2018. The postlaunch calibration algorithm has been revisited by retrieving all of the calibration parameters simultaneously with two different options for the hot calibration source (the global ocean, or the radiometer internal reference load). The performance of the two options are compared here. The option with the radiometer internal reference load has been chosen by the SMAP science team for data release version 5. In addition, a correction offset is applied to the input signal to account for offsets during the early-mission stages with the SMAP synthetic aperture radar transmitter operating alongside the radiometer.

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An improved algorithm for retrieving thin sea ice thickness in the Arctic Ocean from SMOS and SMAP L-band radiometer data

He,

Huang,

Hui

et al. 2024

Acta Oceanol. Sin.

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Soil Moisture Active/Passive (SMAP) L-Band Microwave Radiometer Post-Launch Calibration Upgrade

Cited by 18 publications

References 15 publications

The Use of SMAP-Reflectometry in Science Applications: Calibration and Capabilities

The Use of SMAP-Reflectometry in Science Applications: Calibration and Capabilities

Soil Moisture Active/Passive (SMAP) L-Band Microwave Radiometer Post-Launch Calibration Revisit: Approach and Performance

An improved algorithm for retrieving thin sea ice thickness in the Arctic Ocean from SMOS and SMAP L-band radiometer data

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