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SMAPVEX08 PALS Brightness Temperature Data, Version 1
This data set contains brightness temperatures obtained by the Passive Active L-band System (PALS) microwave aircraft radiometer instrument as part of the Soil Moisture Active Passive Validation Experiment 2008 (SMAPVEX08).
Geographic Coverage
Spatial Coverage: |
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Spatial Resolution: |
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Temporal Coverage: |
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Temporal Resolution: | 1 day to 3 day |
Parameter(s): |
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Platform(s) | AIRCRAFT |
Sensor(s): | PALS |
Data Format(s): |
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Version: | V1 |
Data Contributor(s): | Yueh, S. |
Metadata XML: | View Metadata Record |
Data Citation
As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.
Yueh, S. 2015. SMAPVEX08 PALS Brightness Temperature Data, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/C1FCK9A0317Y. [Date Accessed].Detailed Data Description
This data set contains brightness temperatures obtained by the Passive Active L-band System (PALS) microwave aircraft radiometer instrument as part of the Soil Moisture Active Passive Validation Experiment 2008 (SMAPVEX08).
Table 1 provides descriptions for each column in the data files. An associated Extensible Markup Language (XML) metadata file is also provided for each data file.
Column Number | Description |
---|---|
1 | GMT hour of the day (decimal) |
2 | Latitude of the footprint center [°] |
3 | Longitude of the footprint center [°] |
4 | Incidence angle [°] |
5 | Vertically polarized brightness temperature [K] |
6 | Horizontally polarized brightness temperature [K] |
7 | Infrared surface temperature [°C] |
8 | Place holder (Note: Values for place holders vary). |
9 | Place holder (Note: Values for place holders vary). |
10 | The third Stokes parameter (to be calibrated) |
11 | 1 for RFI and 0 for no RFI based on median filtering for TBv and threshold |
12 | 1 for RFI and 0 for no RFI based on median filtering for TBh and threshold |
13 | 1 for RFI and 0 for no RFI based on median filtering for TBv-TBh and threshold |
Data files are available on the HTTPS site in the https://n5eil01u.ecs.nsidc.org/SMAP_VAL/SV08PLTB.001/
directory.
Files are named according to the following convention and as described in Table 2.
Example File Name: 09291259jv1.txt
MMDDhhmmjv1.txt
Where:
Variable | Description |
---|---|
MM |
2-Digit Month |
DD |
2-Digit Day |
hh |
2-digit hour of the start time |
mm |
2-digit minutes of the start time |
jv1 |
(unknown) |
.txt |
Indicates this is a text file |
Files range in size from approximately 1 to 2.2 MB.
The approximate volume for this data set is 67 MB.
Southernmost Latitude: 38.93°N
Northernmost Latitude: 39.09°N
Westernmost Longitude: 76.25°W
Easternmost Longitude: 75.55°W
Spatial Resolution
The 3dB spatial resolutions of the instruments at two potential altitudes are 350 m (1000 m altitude, minimum for the radar operation) and 1100 m (3000 m, maximum).
Projection Description
Latitude/longitude are provided in World Geodetic System 1984 (WGS84) coordinates.
Data were collected every 1 to 3 days from 29 September 2008 through 13 October 2008.
Parameters include brightness temperature [K], incidence angle [°], and surface temperature [°C].
Parameter Range
Valid parameter values are as follows:
Brightness temperature: 50 - 350 K
Incidence angle: 30° - 50°
Surface temperature: 0 - 40° C
Software and Tools
Any word-processing program or Web browser is sufficient for viewing the ASCII text files.
The quality of the brightness temperature data relies on internal calibration that utilize matched loads and external calibration that exploits lake surfaces close to the experiment area. These references assure good quality of the data.
Data Acquisition and Processing
Current microwave models and retrieval algorithms have significant limitations in their treatment of different vegetation types and heterogeneous scenes (mixtures of grass, crops, trees, streams, lakes) and quantitative treatment of algorithm scaling and error analysis for such heterogeneous scenes. Measurements over wide varieties of terrain are needed, with joint active and passive sensors, to develop algorithms and parameterizations that can work across all terrain types, and extract optimum information from the combined data. This will have direct impact on the design of dedicated soil moisture missions and development of methods to assimilate such data into land surface models.
Microwave radiometry and radar are well-established techniques for surface remote sensing. Combining passive and active sensors provides complementary information contained in the surface emissivity and backscatter signatures, which can improve the accuracy of retrieval of geophysical parameters. Over land, it has been demonstrated that the radiometer and the radar both provide information for estimating soil moisture and vegetation water content (Bolten et al. 2003, Njoku et al. 2002, Narayan et al. 2004).
Error Sources
There are no exceptional error sources for this data set.
The campaign deployed the Jet Propulsion Laboratory (JPL), with NASA support, designed, built and tested a precision Passive Active L-band System (PALS) microwave aircraft instrument for measurements of soil moisture and ocean salinity (Wilson et al. 2001). PALS provides radiometer products, vertically and horizontally polarized brightness temperatures, and radar products, normalized radar backscatter cross-section for V- transmit/V-receive, V-transmit/H-receive, H-transmit/H-receive, and H-transmit/V-receive. In addition, it can also provide the polarimetric third Stokes parameter measurement for the radiometer and the complex correlation between any two of the polarized radar echoes (VV, HH, HV and VH). The following table provides the key characteristics of PALS:
Passive | Frequency | 1.413 GHz |
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Polarization | V, H, +45, -45 | |
Calibration stability | 1 K (bias); 0.2 K (stability) | |
Active | Frequency | 1.26 GHz |
Polarization | VV, HH, VH, HV | |
Calibration accuracy | <2 dB (bias); 0.2 dB (stability) | |
Antenna | Half Power Beamwidth | 20° (passive); 23°(active) |
Beam Efficiency | 94% | |
Directivity | 18.5 dB | |
Polarization isolation | > 35 dB |
PALS was flown in three major soil moisture experiments (SGP99, SMEX02 and CLASIC) before deployment in SMAPVEX08. Beginning with CLASIC, a new flat-panel antenna array was substituted for the large horns. The planar antenna consists of 16 stacked-patch microstrip elements arranged in four-by-four array configurations. Each stacked-patch element uses a honeycomb structure with extremely low dielectric loss at L-band to support the ground plane and radiating patches. The measured antenna pattern shows better than 35 dB polarization isolation, far exceeding the need for the polarimetric measurement capability. This compact, lightweight antenna has enabled PALS to transition to operating on small aircraft, such as the Twin Otter.
Since the CLASIC experiment in 2007, the PALS was augmented with additional components designed to detect and mitigate Radio Frequency Interference (RFI). The demonstration and evaluation of these elements was an important consideration in the SMAPVEX08 design.
PALS was mounted at a 40° incidence angle looking to the rear of the aircraft. The 3dB spatial resolutions of the instruments at two potential altitudes are 350 m (1000 m altitude, minimum for the radar operation) and 1100 m (3000 m, maximum). It is important to note that PALS provides a single beam of data along a flight track and that any mapping must rely upon multiple flight lines at a spacing of the footprint width.

References and Related Publications
Contacts and Acknowledgments
Simon Yueh
Jet Propulsion Laboratory
California Institute of Technology
4800 Oak Grove Dr, Pasadena, CA 91109 USA
Document Information
DOCUMENT CREATION DATE
June 2015
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