Data Set ID: 

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).

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Geographic Coverage

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  • Microwave > Brightness Temperature
  • Microwave > Incidence Angle
  • Land Temperature > Land Surface Temperature
Spatial Coverage:
N: 39.09, 
S: 38.93, 
E: -75.55, 
W: -76.25
Spatial Resolution:
  • 1100 m x 350 m
Temporal Coverage:
  • 29 September 2008 to 13 October 2008
Temporal Resolution: 1 day to 3 days
Data Format(s):
  • ASCII Text
Platform(s) AIRCRAFT
Sensor(s): PALS
Version: V1
Data Contributor(s): Yueh, S.

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: [Date Accessed].

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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.

Table 1. Data Column Descriptions
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
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File and Directory Structure

Data files are available at:

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File Naming Convention

Files are named according to the following convention and as described in Table 2.



Table 2. Data Column Descriptions
Variable Description
SV08PLTB Data Set ID
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

Example File Name: SV08PLTB_09291259jv1.txt

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File Size

Files range in size from approximately 1 to 2.2 MB.

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The approximate volume for this data set is 67 MB.

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Spatial Coverage

Southernmost Latitude: 38.93°N
Northernmost Latitude: 39.09°N
Westernmost Longitude: 76.25°W
Easternmost Longitude: 75.55°W

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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).

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Temporal Coverage and Resolution

Data were collected every 1 to 3 days from 29 September 2008 through 13 October 2008.

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Latitude/longitude are provided in World Geodetic System 1984 (WGS84) coordinates.

Grid Description

No grid.

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Parameter or Variable

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

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Software and Tools

Any word-processing program or Web browser is sufficient for viewing the ASCII text files.

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Data Acquisition and Processing

Theory of Measurements

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).

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Sensor or Instrument Description

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:

Table 3. Description of the PALS instrument
Passive Frequency 1.413 GHz
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.

SMAP PALS Instrument Image
Figure 1. Images of Three Different Aircraft Installations of the PALS Combined Active and Passive L-band Instrument
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Error Sources

There are no exceptional error sources for this data set.

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Quality Assessment

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.

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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


June 2015



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