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Data Set ID:
NSIDC-0666

PALS Soil Moisture Experiment (1999-2008) 800 m Earth-Fixed Grid Brightness Temperature and Backscatter Match-Up, Version 1

This data set contains match‐up data obtained by the Passive Active L‐ and S‐band (PALS) microwave aircraft instrument. The data were collected as part of four different campaigns: Southern Great Plains 1999 (SGP99), Cloud and Land Surface Interaction Campaign 2007 (CLASIC 2007), Soil Moisture Experiment 2002 (SMEX02), and the SMAP Validation Experiment 2008 (SMAPVEX08).

Version Summary:

First public data release.

Geographic Coverage

Spatial Coverage:
  • N: 39.09, S: 38.95, E: -75.54, W: -76.18

  • N: 41.99, S: 41.92, E: -93.4, W: -93.8

  • N: 35.21, S: 34.91, E: -97.83, W: -98.67

Spatial Resolution:
  • 800 m x 800 m
Temporal Coverage:
  • 8 July 1999 to 14 July 1999
  • 25 June 2002 to 8 July 2002
  • 11 June 2007 to 6 July 2007
  • 29 September 2008 to 13 October 2008
Temporal Resolution: 1 day to 3 day
Parameter(s):
  • Microwave > Brightness Temperature
  • Microwave > Brightness Temperature > Incidence Angle
  • Land Use/Land Cover > Land Use Classes > Land Cover
  • Radar > Radar Backscatter > Normalized Radar Cross-Section
  • Soils > Soil Temperature
  • Vegetation > Plant Characteristics > Vegetation Water Content
Platform(s) AIRCRAFT
Sensor(s): PALS
Data Format(s):
  • ASCII Text
Version: V1
Data Contributor(s): Colliander, A.

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.

Colliander, A. 2016. PALS Soil Moisture Experiment (1999-2008) 800 m Earth-Fixed Grid Brightness Temperature and Backscatter Match-Up, 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/MPSKZBVINW95. [Date Accessed].

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Notice: 
The documentation for this data set was provided solely by the Principal Investigator(s) and was not further developed, thoroughly reviewed, or edited by NSIDC. Thus, support for this data set may be limited.

If you have any questions, please contact:

Andreas Colliander
Jet Propulsion Laboratory
California Institute of Technology
4800 Oak Grove Dr., M/S 300‐233
Pasadena, CA 91109 USA

andreas.colliander[at]jpl.nasa.gov

Detailed Data Description

This data set contains match‐up data obtained by the Passive Active L‐ and S‐band (PALS microwave aircraft instrument. The data were collected as part of four different campaigns: Southern Great Plains 1999 (SGP99), Cloud and Land Surface Interaction Campaign 2007 (CLASIC 2007), Soil Moisture Experiment 2002 (SMEX02), and the SMAP Validation Experiment 2008 (SMAPVEX08). The data set covers four different periods ranging from 1999 through 2008 corresponding with the four soil moisture campaigns.

Format

Data are in column‐ordered ASCII text format. Table 2 provides descriptions for each column in the data file, in addition to parameter units and values. 

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File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/smap_data/validation_data/PALS_SM_99‐08/earth_grid_matchup/ directory. Within this directory, there is one file: matchup_pals_grid_v107_111012.txt.

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File Naming Convention

This section explains the file naming convention used for this product with an example.

Example File Name: matchup_pals_grid_v107_111012.txt

matchup_pals_grid_vXXX_YYMMDD.txt

Refer to Table 1 for the valid values for the file name variables listed above.

Where:

Table 1. File Naming Convention

Variable

Description

vXXX

3‐Digit Match‐Up Version 

YYMMDD

2‐Digit Year, Month, and Day 

.txt

Indicates this is a text file 

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File Size

The file is approximately 3.5 MB.

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Spatial Coverage

The following study areas correspond with the four different soil moisture campaigns: 

Oklahoma (SGP99, CLASIC)

Southernmost Latitude: 34.91ºN
Northernmost Latitude: 35.21ºN
Westernmost Longitude: 98.67ºW
Easternmost Longitude: 97.83ºW

Iowa (SMEX02)

Southernmost Latitude: 41.92ºN
Northernmost Latitude: 41.99ºN
Westernmost Longitude: 93.80ºW
Easternmost Longitude: 93.40ºW

Maryland (SMAPVEX08)

Southernmost Latitude: 38.95ºN
Northernmost Latitude: 39.09ºN
Westernmost Longitude: 76.18ºW
Easternmost Longitude: 75.54ºW

Spatial Resolution

The spatial resolution is 800 m

Projection/Grid Description

The study areas fall in the following UTM (WGS84) grid zones:
Oklahoma: 14 N
Iowa: 15 N
Maryland: 18 N

There are five separate grids in the data, each corresponding to a study area. Table 2 shows the number of rows and columns in each grid. In the file the data are ordered column‐wise southto‐north, west‐to‐east. Thus, when data are searched for a given area on a given date, a collection of data points is returned which can be ordered as grid—the size of which is given in Table 2. Note that the file includes coordinates for each data point, which can be used to validate that the grid is formed correctly.   

Table 2. Description of Grids

Field Campaign(s)

Study Area

Number of rows in the grid

Number of columns in the grid

Number of entries per day

Area Code

SMAPVEX08

Choptank (Maryland)

20

70

1400

020

SGP99

Little Washita (Oklahoma)

9

52

468

060

CLASIC 2007

Fort Cobb (Oklahoma)

4

35

140

050

CLASIC 2007

Little Washita (Oklahoma)

8

63

504

060

SMEX02

Walnut Creek (Iowa)

10

43

430

070

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Temporal Coverage

SGP99: 8 – 14 July 1999
SMEX02: 25 June – 8 July 2002
CLASIC 2007: 11 June – 6 July 2007
SMAPVEX08: 29 September – 13 October 2008

Temporal Resolution

Measurements were collected on the following days:
SGP99: 8, 9, 11, 12, 13, 14 July
SMEX02: 25, 27 June; 1, 2, 5, 6, 7, 8 July
CLASIC: 11, 12, 19, 23, 24, 25 June; 1, 3, 4, 5, 6 July
SMAPVEX08: 29 Sep; 2, 4, 6, 8, 10, 13 Oct

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Parameter or Variable

Table 3 summarizes parameters and lists units and ranges. For detailed descriptions of parameters, see the Parameter Description section.  

Table 3. Column Description with Parameter Units and Value Ranges

Column

Description

Unit

Range

1

Year

N/A

1999‐ 2008

2

Month of year

N/A

1‐12

3

Day of month

N/A

1‐31

4

Day of year

N/A

1‐365

5

Area code (e.g. Walnut Creek = 070)

N/A

20‐70

6

Easting of grid point

M

3∙105‐7∙105

7

Northing of grid point

M

3∙106‐5∙106

8

Radiometer (L‐band) V‐pol calibrated brightness temperature (TB)

K

100‐300

9

Radiometer (L‐band) H‐pol calibrated brightness temperature (TB)

K

100‐300

10

Radiometer beam mean incidence angle

Deg

35‐45

11

Radar (L‐band) VV‐pol radar backscatter (sigma 0)

dB

‐25 ‐ ‐3

12

Radar (L‐band) HH‐pol radar backscatter (sigma 0)

dB

‐25 ‐ ‐3

13

Radar (L‐band) VH‐pol radar backscatter (sigma 0)

dB

‐37 ‐ ‐14

14

Radar (L‐band) HV‐pol radar backscatter (sigma 0)

dB

‐37 ‐ ‐14

15

Radar beam mean incidence angle

Deg

35‐45

16

In situ soil moisture (where available)

cm3/cm3

0‐0.6

17

Airborne (IR) surface temperature (nadir)

°C

10‐50

18

In situ (IR) surface temperature (where available)

°C

10‐50

19

Soil temperature at depth of 1cm (where available)

°C

10‐50

20

Soil temperature at depth of 5cm (where available)

°C

10‐50

21

Vegetation Water Content from field sampling (where available)

kg/m2

0‐7

22

Vegetation Water Content from NDVI

kg/m2

0‐7

23

Land cover class (MODIS IGBP)

N/A

0‐255

24

Crop type

N/A

0‐7

25

Clay percentage

%

0‐100

26

Sand percentage

%

0‐100

27

Performance flag 1: 

1 when STD(TB) < 4 K and STD(S0) < 2 dB, otherwise 0

N/A

0,1

28

Performance flag 2: 

1 when STD(TB) < 8 K and STD(S0) < 4 dB, otherwise 0

N/A

0,1

Parameter Description

Time stamp (columns 1‐4)

The data are time stamped based on the day of the PALS and in situ measurements: year, month of the year, day of the month and day of the year are included.

Areas and coordinates (columns 5‐7)

The study areas of different campaigns are coded based on the study areas as listed in Table 2, and correspond with the grids. The grid points are defined at the center of the grid cell. The size corresponds to the grid of the particular study area. Each grid appears in column‐wise order in the data. Users should fill the matrix in column‐by‐column order, such as when a data field

For example, V‐pol brightness temperatures for any given campaign day such as 1 July 2002 is selected the resulting vector can be ordered in a matrix. Based on Table 2 for SMEX02, the size of the matrix would be 10 by 43 (the coordinates on columns 6 and 7 can be used to check that the grid is formed correctly).

Brightness Temperature (columns 8‐9)

L‐band Brightness Temperature acquired with PALS. The configuration of PALS depends on the campaign. The data include vertically and horizontally polarized brightness temperatures. The flight altitude and antenna of the instrument vary from campaign to campaign. These differences have an effect on the consistency of the combined data record. Refer to the Data Acquisition and Processing section of this guide document.

Normalized Radar Cross Section (columns 11‐14)

L‐band Normalized Radar Cross Section (NRCS) acquired with PALS. The configuration of PALS depends on the campaign. The data include the following polarizations: V‐pol transmit/V‐pol receive, V‐pol transmit/H‐pol receive, H‐pol transmit/H‐pol receive, H‐pol transmit/V‐pol receive. The flight altitude and antenna of the instrument vary from campaign to campaign.  These differences have an effect on the consistency of the combined data record. Refer to the Data Acquisition and Processing section of this guide document.

PALS incidence angles (columns 10 and 15)

The incidence angle of the PALS measurements over each grid cell is obtained using the aircraft attitude.

In situ soil moisture (columns 16)

When a grid cell coincides with an in situ sample of soil moisture, the in situ soil moisture value is included in the data. Different methods are used in different campaigns which have an effect on the consistency of the combined data record. Refer to the Data Acquisition and Processing section of this guide document.

Infrared surface temperature from in situ measurements (columns 17)

When a grid cell coincides with an in situ sample of surface temperature, the in situ surface temperature value is included in the data.

Infrared surface temperature from airborne measurements (columns 18)

The measurement with the nadir pointing infrared sensor mounted on the same aircraft as PALS.

Soil temperature (columns 19 and 20)

When a grid cell coincides with in situ samples of soil temperature (at 1 cm and/or 5 cm depths), the in situ soil temperature values are included in the data.

Vegetation Water Content (VWC) from in situ measurements (columns 21)

When a grid cell coincides with an in situ sample of VWC, the in situ VWC is included in the data.

Vegetation Water Content (VWC) from satellite measurements of NDVI (columns 22)

Satellite‐based NDVI resolved from acquisitions that were acquired in the time frame of the campaign are used to calculate VWC. The availability and quality of satellite observations vary from campaign to campaign.  The difference in availability and quality has an effect on the consistency of the combined data record (see Section 4 for details).

Land Cover (columns 23 and 24)

The land cover classification follows the MODIS IGBP classes (see Table 4). The crop type is further specified for agricultural class (see Table 5).

Land cover class

Code

Table 4. Land Cover Classes

Water

0

Evergreen Needle leaf Forest

1

Evergreen Broadleaf Forest

2

Deciduous Needle leaf Forest

3

Deciduous Broadleaf Forest

4

Mixed Forests

5

Closed Shrub lands

6

Open Shrub lands

7

Woody Savannas

8

Savannas

9

Grasslands

10

Permanent Wetlands

11

Croplands

12

Urban and Built‐Up

13

Cropland/Natural Vegetation Mosaic

14

Permanent Snow and Ice

15

Barren or Sparsely Vegetated

16

Fill Value

255

Crop Type Code
Table 5. Crop Type
N/A 0
Bare 1
Alfalfa 2
Corn 3
Soy 4
Wheat 5
Legume 6
Cotton 7

Soil texture (columns 25 and 26)

Ancillary data sources provide the sand and clay fraction for the study areas (refer to the Clay and Sand Percentages heading in the Data Acquisition and Processing section of this guide document. 

Performance flags (columns 27 and 28)

The flags indicate the level of variance as standard deviation in the samples used to obtain a particular grid cell value. 

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Software and Tools

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

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Data Acquisition and Processing

Theory of Measurements

The data combine a suite of measurements collected in four different airborne soil moisture retrieval algorithm development campaigns: SGP99, SMEX02, CLASIC 2007, and SMAPVEX08. The goal of the campaigns was to obtain data that can be used to develop soil moisture retrieval algorithms based on microwave observations. Each campaign deployed an airborne instrument called PALS (Passive Active L‐band System), and this data set combines the PALS observations with a set of ground truth collected in those campaigns. 

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Derivation Techniques and Algorithms

Brightness temperature (cols 8‐9)

The vertical and horizontal brightness temperature value is computed by averaging all brightness temperature values falling within a grid cell. The same procedure is applied to all campaigns. The standard deviation of the averaged set of data are also computed for performance evaluation and setting the performance flags.

Normalized radar cross section (cols 11‐14)

The radar cross‐section value for different polarization combinations are computed by averaging (in linear scale) all radar cross‐section values falling within a grid cell. The same procedure is applied to all campaigns. The standard deviation of the averaged set of data are also computed for performance evaluation and setting the performance flags.

PALS incidence angles (cols 10 and 15)

The incidence angle of the PALS measurements over each grid cell is obtained from the PALS data and averaged along with the brightness temperature and radar backscatter cross‐section.

Volumetric soil moisture (col 16)

SGP99

Volumetric soil moisture estimates are based on thermo‐gravimetric method. The gravimetric soil moisture was measured at all in situ sites of the campaign on each day of the PALS flights. The match‐up uses these values for corresponding days of the campaign. The bulk density of the soil of each in situ site was also determined (once) and that was used to determine the volumetric soil moisture corresponding to the gravimetric measurements.

SMEX02

Each in situ site was sampled with several soil moisture probe measurements on each day of PALS flights. The match‐up uses the averaged value of these samples. The probe measurements were calibrated with occasional thermo‐gravimetric measurements.

Each in situ site was sampled with several soil moisture probe measurements on each day of PALS flights. The match‐up uses the averaged value of these samples. The probe measurements were calibrated with occasional thermo‐gravimetric measurements.

SMAPVEX08

Each in situ site was sampled with several soil moisture probe measurements on each day of PALS flights. The match‐up uses the averaged value of these samples. The probe measurements were calibrated with occasional thermo‐gravimetric measurements.

Infrared Surface Temperature: Airborne and In Situ (cols 17‐18)

The physical temperature of the surface was measured by both airborne and handheld infrared sensor (for CLASIC campaign the airborne infrared data are to be processed).

The handheld measurement is applicable to ground skin temperature whereas the airborne measurement is applicable to the skin temperature of the field of view from the aircraft, which may include vegetation.

Soil Temperatures at 1‐cm and 5‐cm Depths (cols 19‐20)

The physical temperature of the soil was measured in each campaign at the soil moisture in situ sites at depths of 1 cm and 5 cm on each day of PALS flights.

Vegetation Water Content (VWC): in situ (col 21)

VWC was retrieved from optical satellite measurements for some of the campaigns.

SGP99

Vegetation water content was determined one time for each in situ site during the campaign. The match‐up uses this value for each day of the campaign. Measurement dates vary from field to field for any given campaign, and are included in the data file.

SMEX02

Vegetation water content was determined for each in situ site 2 to 4 times during the campaign. The match‐up uses the value which was obtained closest to the respective flight date.

CLASIC

No in situ vegetation water content information is available.

SMAPVEX08

Vegetation water content was determined at 8 sites one time during the campaign. The match up uses these values for these sites for each day of the campaign.

Vegetation Water Content (VWC): satellite derived (col 22)

VWC was retrieved from optical satellite measurements for some of the campaigns. 

SGP99

NDVI data are available but processing for VWC has not been done so far.

SMEX02

Several NDWI measurements over the course of the campaign were used to apply a model to map the VWC over the in situ sites. The VWC was interpolated to cover all measurement days. The match‐up uses the interpolated VWC values for the respective flight dates.

CLASIC

One‐time NDWI image was used to obtain the vegetation water content. The values are based on images obtained on 15 July 2007. The match‐up uses this value for each day of the campaign. The conditions for VWC were less than optimal due to cloud cover over the test sites during the campaign. Caution is advised when interpreting these data.

SMAPVEX08

One‐time NDWI image was used to obtain the vegetation water content. The match‐up uses this value for each day of the campaign.

Land Cover (cols 23‐24)

The land cover over the in situ sites was determined based on the land classification maps, except for CLASIC, in which case the in situ records were utilized. The crop classification of the agricultural fields is based on the in situ records.

Clay and Sand Percentages (cols 25‐26)

The derivation of the clay and sand percentages for each campaign is explained below.

SGP99

The clay and sand fractions are obtained from the online database hosted by the Earth System

Science Center in the College of Earth and Mineral Sciences at The Pennsylvania State University (www.soilinfo.psu.edu). The data are from CONUS‐SOIL, a multi‐layer soil characteristics data set for the conterminous United States based on the USDA State Soil Geographic Database (STATSGO). A subset of this data was extracted for the SGP region. The resolution of the data is 30 arc seconds. The data pixel closest to a given in situ site was selected to represent the clay and sand fractions of that in situ site. The same STATSGO database was used also for CLASIC campaign in situ sites.

SMEX02

SMEX02 data set on the NASA DAAC (nsidc.org/data/amsr_validation/soil_moisture/smex02/) includes the clay and sand fractions for the campaign region. The data are given in shape file (.shp) format. The shape files give the upper and lower limit of the fraction within each shape. For a given in situ site the clay and sand fractions are determined by averaging the upper and lower limits of the fractions given in the shapes falling within the defined pixel size from the coordinate of the site.

CLASIC

The clay and sand fractions are obtained from the online database hosted by the Earth System

Science Center in the College of Earth and Mineral Sciences at The Pennsylvania State University (www.soilinfo.psu.edu). The data are from CONUS‐SOIL, a multi‐layer soil characteristics data set for the conterminous United States based on the USDA State Soil Geographic Database (STATSGO). A subset of this data was extracted for the SGP region. The resolution of the data is 30 arc seconds. The data pixel closest to a given in situ site was selected to represent the clay and sand fraction of that in situ site. The same data was used also for SGP99 campaign in situ sites.

SMAPVEX08

The clay and sand fractions for the SMAPVEX08 campaign were pre‐processed by USDA‐ARS based on the online database hosted by the Earth System Science Center in the College of Earth and Mineral Sciences at The Pennsylvania State University (www.soilinfo.psu.edu). The data are from CONUS‐SOIL, a multi‐layer soil characteristics data set for the conterminous United States based on the USDA State Soil Geographic Database (STATSGO). The pre‐processed data covers the SMAPVEX08 region in 100 meter resolution. The average of the clay and sand fraction within the defined pixel size was calculated to represent the respective in situ site.

Performance flags (cols 27‐28)

Two performance flags are given with the data. The flags indicate the level of variance in the samples used to obtain a particular grid cell value. They are determined based on the Standard Deviation (STD) computed from the set of brightness temperatures and radar cross‐section samples falling within the given grid cell.

The first one indicates whether the STD of the brightness temperatures of both polarizations is less than 2 K and the STD of both HH‐ and VV‐polarized radar cross‐sections is less than 4 dB. If so, the flag is 1. The flag is 0 in any other case.

The second one indicates whether the STD of the brightness temperatures of both polarizations is less than 4 K and the STD of both HH‐ and VV‐polarized radar cross‐sections is less than 8 dB. If so, the flag is 1. The flag is 0 in any other case.

Error Sources

There are no exceptional error sources for this data set.

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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/S‐band (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/Hreceive, 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 6. 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 degree 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.

Figure 1. Active and Passive L-Band Instrument Descriptions
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References and Related Publications

Contacts and Acknowledgments

Investigator

Andreas Colliander
Jet Propulsion Laboratory
California Institute of Technology
4800 Oak Grove Dr., M/S 300‐233
Pasadena, CA 91109 USA
andreas.colliander[at]jpl.nasa.gov

Document Information

DOCUMENT CREATION DATE

February 2016

No technical references available for this data set.
No FAQs or How Tos available for this data set.

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