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SMEX02 Passive and Active L and S band System (PALS) Data

Summary

This data set contains calibrated sensor measurements acquired by the Passive and Active L- and S-band (PALS) airborne microwave sensor during the Soil Moisture Experiment 2002 (SMEX02). This data set includes radiometer brightness temperatures (TB) at 1.41 and 2.69 GHz, and radar backscatter coefficients at 1.26 and 3.15 GHz, with multiple polarizations and a 45° incidence angle. The data are geolocated with latitude and longitude information for each data sample. Included are coregistered nadir and boresight infrared temperatures, altitude, and attitude information. Radar and radiometric studies are relevant to SMEX02 because the data indicates wet soil versus dry soil based on differences in emissivity in the microwave spectral region.

Data are provided as ASCII files for each flight line and day of the mission. Ten flight lines were flown each day. Flights took place on June 25, 27, and July 1, 2, 5, 6, 7, 8 2002. Data are available via FTP.

These data were collected as part of a validation study for the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E). AMSR-E is a mission instrument launched aboard NASA's Aqua Satellite on 04 May 2002. AMSR-E validation studies linked to SMEX are designed to evaluate the accuracy of AMSR-E soil moisture data. Specific validation objectives include assessing and refining soil moisture algorithm performance; verifying soil moisture estimation accuracy; investigating the effects of vegetation, surface temperature, topography, and soil texture on soil moisture accuracy; and determining the regions that are useful for AMSR-E soil moisture measurements.

Citing These Data

Njoku, E. G. 2003. SMEX02 Passive and Active L and S band System (PALS) Data. [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center.

Overview Table

Category Description
Data format Data are provided as ASCII text files or as two tar files that contain the text files.
Spatial coverage and resolution 42° N, 93° W
Temporal coverage and resolution Daily coverage for June 25, 27, and July 1, 2, 5-8 2002
File naming convention All file names consist of month, day, and hour in the form: MMDDHHHH. The Radar files have a ".red" file extension to distinguish them from the radiometric files, which have a ".txt" extension. For example, "06250841.red" is the radar file, and "06250841.txt" is the radiometric file. Data for both files was obtained on 6 June at 08:41.
File size File size ranges from 7 KB to 220 KB.
Parameter(s) Radiometer brightness temperatures (TB) at 1.41 and 2.69 GHz
Radar backscatter coefficients at 1.26 and 3.15 GHz

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments

Investigator(s) Name and Title

Eni Njoku, Research Scientist, Jet Propulsion Laboratory, Pasadena, California, USA.

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

Acknowledgements

William J. Wilson, Simon. H. Yueh, and Steven J. Dinardo, Jet Propulsion Laboratory

2. Detailed Data Description

PALS is a non-scanning, real-aperture, combined microwave radiometer and radar. The radiometer operates at 1.41 and 2.69 GHz; the radar at and 1.26 and 3.15 GHz. The radiometer operates at V (vertical) and H (horizontal) polarizations, while the radar operated at VV, HH, and VH polarizations. Two conical horn antennas were used. An L-band horn of 1.2 m diameter was shared between the 1.41 and 1.26 GHz radiometer and radar frequencies. An S-band horn of 0.54 m diameter was shared between the 2.69 and 3.15 GHz radiometer and radar frequencies.

The PALS instrument was designed for flight on a C-130 aircraft, with the antennas installed on the rear ramp, viewing downwards to the rear of the aircraft. The antennas were set to view the surface at a constant incidence angle of 45°. The instrument sampled a single footprint track along the flight path. In SMEX02 PALS was operated nominally at ~3500 feet, with one set of flights (6 July) at ~7000 feet.

Format

Data are provided as ASCII text files or as two tar files that contain the text files.

File and Directory Structure

Data are contained in two directories. The directory "radr" contains the radar files. The directory "radm" contains the radiometric files.

File Naming Convention

All file names consist of month, day, and hour in the form: MMDDHHHH. The Radar files have a ".red" file extension to distinguish them from the radiometric files, which have a ".txt" extension. For example, "06250841.red" is the radar file, and "06250841.txt" is the radiometric file. Data for both files was obtained on 6 June at 08:41.

File Size

File size ranges from 7 KB to 220 KB.

Spatial Coverage

Southernmost Latitude: 41.9213° N
Northernmost Latitude: 41.9952° N
Westernmost Longitude: 93.7750° W
Easternmost Longitude: 93.4013° W

Spatial Resolution

Each sample has a footprint resolution of approximately 330 x 470 m.

Temporal Coverage

25 June through 8 July 2002.

Temporal Resolution

Daily coverage for June 25, 27, and July 1, 2, 5-8 2002.

Parameter or Variable

Parameter Range

The following tables explain the columns in the data files. The first table defines the columns in the radiometric files found in the "radm" directory.

Column heading Description (unit of measure)
time Instrument local time from midnight(sec)
L-H L-band H-pol calibrated brightness temperature (TB) (K)
L-V L-band V-pol calibrated TB (K)
S-H S-band H-pol calibrated TB (K)
S-V S-band V-pol calibrated TB (K)
boresight Thermal infrared surface temperature (boresight camera) (°C)
nadir Thermal infrared surface temperature (nadir camera) (°C)
ant_angle Antenna beam incidence angle (deg)(nominally 45°)
roll_angle Aircraft roll angle (deg)
lat Footprint center latitude (deg) (corrected for aircraft altitude and attitude)
long Footprint center longitude (deg) (corrected for aircraft altitude and attitude)
ant_azimuth Antenna azimuth viewing angle relative to North (deg) (East is 90 deg)
altitude Aircraft altitude (m)
sample# Sample number in original instrument data record

The next table defines the columns in the radar files found in the "radr" directory.

Column heading Description (unit of measure)
time Instrument local time from midnight (sec)
GPS_time Aircraft GPS time (UT) from midnight (sec)
lat Footprint center latitude corrected for altitude and attitude (deg)
long Footprint center longitude corrected for altitude and attitude(deg)
ant_azimuth Antenna azimuth viewing angle relative to North (deg) (East is 90°)
polar_angle Antenna polarization rotation angle (deg)(Angle of the V and H polarizations of the horn antennas relative to nominal)
range Range from surface footprint to aircraft (m)
beam_angle Antenna beam incidence angle (deg) (nominally 45 degrees)
L_HH L-band HH-pol radar backscatter (sigma 0) (dB)
L_VV L-band VV-pol radar backscatter (sigma 0) (dB)
L_VH L-band VH-pol radar backscatter (sigma 0) (dB)
L_HV L-band HV-pol radar backscatter (sigma 0) (dB)
S_HH S-band HH-pol radar backscatter (sigma 0) (dB)
S_VV S-band VV-pol radar backscatter (sigma 0) (dB)
S_VH S-band VH-pol radar backscatter (sigma 0) (dB)
S_HV S-band HV-pol radar backscatter (sigma 0) (dB)
LR_HHVV Normalized real part of L-band HH and VV complex correlation
LI_HHVV Normalized imaginary part of L-band HH and VV complex correlation
LR_HHVH Normalized real part of L-band HH and VH complex correlation
LI_HHVH Normalized imaginary part of L-band HH and VH complex correlation
LR_HHHV Normalized real part of L-band HH and HV complex correlation
LI_HHHV Normalized imaginary part of L-band HH and HV complex correlation
LR_VVVH Normalized real part of L-band VV and VH complex correlation
LI_VVVH Normalized imaginary part of L-band VV and VH complex correlation
LR_HVVV Normalized real part of L-band HV and VV complex correlation
LI_HVVV Normalized imaginary part of L-band HV and VV complex correlation
LR_HVVH Normalized real part of L-band HV and VH complex correlation
LI_HVVH Normalized imaginary part of L-band HV and VH complex correlation
SR_HHVV Normalized real part of S-band HH and VV complex correlation
SI_HHVV Normalized imaginary part of S-band HH and VV complex correlation
SR_HHVH Normalized real part of S-band HH and VH complex correlation
SI_HHVH Normalized imaginary part of S-band HH and VH complex correlation
SR_HHHV Normalized real part of S-band HH and HV complex correlation
SI_HHHV Normalized imaginary part of S-band HH and HV complex correlation
SR_VVVH Normalized real part of S-band VV and VH complex correlation
SI_VVVH Normalized imaginary part of S-band VV and VH complex correlation
SR_HVVV Normalized real part of S-band HV and VV complex correlation
SI_HVVV Normalized imaginary part of S-band HV and VV complex correlation
SR_HVVH Normalized real part of S-band HV and VH complex correlation
SI_HVVH Normalized imaginary part of S-band HV and VH complex correlation

Sample Data Record

The following sample is taken from "07060831.txt," a radiometric file acquired 6 July 2002.

time L-H L-V S-H S-V boresight nadir ant_angle roll_angle lat long ant_azimuth altitude sample#
30697.2 260.33 283.13 272.57 286.31 25.1 25.6 44.3 0.3 41.9277 -93.7849 273 1152 44
30698.2 259.71 281.97 273.67 287.22 25.0 25.6 44.3 0.5 41.9277 -93.7838 273 1153 46
30699.2 258.61 280.75 272.89 285.96 24.9 25.7 44.3 1.1 41.9278 -93.7828 273 1154 48
30700.3 257.24 279.87 271.65 283.33 25.4 25.9 44.2 2.0 41.9279 -93.7817 273 1156 50
30701.3 255.91 279.17 270.42 283.18 26.2 26.5 44.2 3.0 41.9279 -93.7804 274 1158 52

The next sample is taken from "07060959.red," a radar file acquired 6 July 2002. This sample does not show every column, but gives an example of the different kinds of data columns.

time GPS_time lat long ant_azimuth polar_angle range beam_angle L_HH L_VV S_HH S_VH S_HV LR_HHVV LI_HHVV SI_HHVH SR_HVVH
35983 53985 41.9845 -93.8238 271.3341 3.84 1609.8 44.52 -10.52 -12.36 -10.62 -19.48 -19.02 0.194 0.037 0.028 0.798
35984 53985 41.9845 -93.8231 271.4243 3.82 1612 44.55 -10.51 -12.87 -10.67 -19.4 -18.89 0.137 0.122 0.028 0.805
35985 53986 41.9845 -93.8226 271.4719 3.8 1612.5 44.55 -10.04 -12.79 -10.67 -19.26 -18.68 0.108 0.299 0.03 0.814
35985 53987 41.9845 -93.8215 271.5459 3.7067 1613.1 44.55 -9.11 -12.59 -10.7 -18.93 -18.29 0.093 0.449 0.033 0.823
35986 53988 41.9846 -93.8204 271.5917 3.57 1613.2 44.55 -8.19 -12.39 -10.7 -18.61 -17.96 0.078 0.59 0.036 0.824

3. Data Access and Tools

Data Access

Access data via FTP.

Related Data Collections

See NSIDC's Soil Moisture Experiment (SMEX) for more information.

4. Data Acquisition and Processing

The following tables define the flight paths covered in each of the data files. The tables are arranged by date, the same as the directory structure.

25 June 2002 Files

Pass# Line# Radiometer Files Radar Files Comments
1 1e 06250752.txt 06250752.red RFI in S-band. Flown at 820-m altitude.
2 1w 06250801.txt 06250801.red RFI in S-band
3 2e 06250812.txt 06250813.red RFI in S-band. Timing computer crash.
4 3e 06250845.txt 06250846.red RFI in S-band.
5 3w 06250854.txt 06250854.red RFI in S-band.
6 4e 06250905.txt 06250905.red RFI in S-band.
7 4w 06250914.txt 06250914.red RFI in S-band.
8 5e 06250925.txt 06250925.red RFI in S-band.
9 5w 06250935.txt 06250935.red
10 6e 06250945.txt 06250945.red
11 6w 06250957.txt 06250957.red
12 7e 06251007.txt 06251007.red
13 7w 06251016.txt 06251016.red
14 8e 06251027.txt 06251027.red
15 8w 06251037.txt 06251037.red
16 9e 06251047.txt 06251047.red
17 9w 06251056.txt 06251056.red
18 10e 06251107.txt 06251107.red
19 10w 06251116.txt 06251116.red
20 2e 06251126.txt Repeat of earlier pass. Radar problem.
21 2w 06251135.txt 06251135.red

27 June 2002 Files

Pass# Line# Radiometer Files Radar Files Comments
1 1e 06270814.txt 06270814.red
2 2w 06270825.txt 06270825.red
3 3e 06270836.txt 06270836.red
4 4w 06270847.txt 06270847.red
5 5e 06270857.txt 06270857.red
6 6w 06270909.txt 06270909.red RFI in LH.
7 7e 06270919.txt 06270919.red
8 8w 06270930.txt 06270930.red RFI in LH. IR camera problem.
9 9e 06270941.txt 06270941.red
10 10w 06270952.txt 06270951.red RFI in LH.
11 06271000.txt 06270959.red Pass over trees.

1 July 2002

Pass# Line# Radiometer Files Radar Files Comments
1 1e 07010833.txt 07010833.red
2 2w 07010845.txt 07010845.red
3 3e 07010857.txt 07010858.red
4 4w 07010907.txt 07010907.red Computer problem, end of day's mission.

2 July 2002

Pass# Line# Radiometer Files Radar Files Comments
1 1e 07020831.txt 07020831.red
2 2w 07020841.txt 07020842.red
3 3e 07020855.txt 07020855.red
4 4w 07020906.txt 07020906.red
5 5e 07020918.txt 07020918.red
6 6w 07020929.txt 07020929.red
7 7e 07020941.txt 07020942.red
8 8w 070020952.txt 07020952.red
9 9e 07021005.txt 07021005.red
10 10w 07021015.txt 07021015.red
11 07021025.txt 07021025.red Pass over trees.

5 July 2002

Pass# Line# Radiometer Files Radar Files Comments
1 1e 07050832.txt 07050832.red
2 1w 07050843.txt 07050843.red
3 2e 07050855.txt 07050855.red
4 2w 07050906.txt 07050906.red
5 3e 07050917.txt 07050917.red
6 3w 07050928.txt 07050928.red
7 4e 07050939.txt 07050939.red
8 4w 07050950.txt 07050950.red
9 5e 07051002.red Radiometer bad acquisition
10 5w 07051013.txt 07051013.red
11 6e 07051024.txt 07051024.red
12 6w 07051034.txt 07051035.red
13 7e 07051046.txt 07051046.red
14 7w 07051056.txt 07051057.red
15 8e 07051108.txt 07051108.red
16 8w 07051118.txt 07051118.red
17 9e 07051130.txt 07051130.red
18 9w 07051141.txt 07051141.red
19 10e 07051152.txt 07051152.red
20 10w 07051202.txt 07051203.red
21 07051212.txt 07051212.red Pass over trees.
22 5e 07051215.txt Repeat radiometer pass aborted earlier.

6 July 2002

Pass# Line# Radiometer Files Radar Files Comments
1 1e 07060831.txt 07060831.red
2 2w 07060840.txt 07060841.red
3 3e 07060852.txt 07060853.red
4 4w 07060902.txt 07060902.red
5 5e 07060914.txt 07060914.red
6 6w 07060924.txt 07060925.red
7 7e 07060936.txt 07060936.red
8 8w 07060947.txt 07060947.red
9 9e 07060059.txt 07060059.red
10 10w 07061009.txt 07061010.red
11 07061019.txt 07061019.red
12 1e 07061028.txt 07061028.red Timing glitch in radiometer.
13 1e 061033.txt Restarted file (lost ~0.5 mins data).
14 2w 07061038.txt 07061038.red
15 3e 07061050.txt 07061050.red
16 4w 07061100.txt 07061100.red
17 5e 07061111.txt 07061111.red
18 6w 07061122.txt 07061122.red
19 7e 07061133.txt 07061133.red
20 8w 07061143.txt 07061143.red
21 9e 07061154.txt 07061154.red
22 10w 07061204.txt 07061204.red

7 July 2002

Pass# Line# Radiometer Files Radar Files Comments
1 1e 07070959.txt 07070959.red
2 2w 07071015.txt 07071015.red
3 3e 07071027.txt 07071027.red
4 4w 07071037.txt 07071037.red
5 5e 07071049.txt 07071049.red
6 6w 07071100.txt 07071100.red
7 7e 07071111.txt 07071111.red
8 8w 07071122.txt 07071122.red
9 9e 07071134.txt 07071134.red
10 10w 07071144.txt 07071144.red
11 07071153.txt 07071153.red Pass over trees.

8 July 2002

Pass# Line# Radiometer Files Radar Files Comments
1 1e 07080817.txt 07080817.red
2 2w 07080827.txt 07080827.red
3 3e 07080841.txt 07080841.red
4 4w 07080851.txt 07080851.red Significant LH RFI.
5 5e 07080905.txt 07080905.red
6 6w 07080915.txt 07080915.red Significant LH RFI.
7 07080926.red Pass over trees.
8 7e 07080929.txt 07080929.red
9 8w 07080938.txt 07080938.red Significant LH RFI.
10 9e 07080952.txt 07080952.red
11 10w 07081001.txt 07081001.red
12 07081012.txt 07081012.red Pass over trees.

Theory of Measurements

To minimize radio-frequency interference (RFI), the PALS radiometers incorporated narrow-band filters at 20 MHz for L-band and 5 MHz fort S-band. At a nominal flight altitude of 1 km and incidence angle of 45° the instantaneous 3-dB footprints at the surface were approximately 330 x 470 m. The received radar and radiometer signals were detected and output by the instrument data system at 0.8-s and 0.5-s intervals, respectively. The radiometer data are further averaged in the post-processing to 1-s intervals. Aircraft location and navigation data and downward-looking thermal IR temperatures were recorded at 1-s intervals and inserted into the PALS data stream.

The radiometric sensitivities, ΔT, for a 1-s integration time are 0.25 K and 0.6 K at L and S bands, respectively. The velocity of the C-130 aircraft was approximately 70 m s-1, resulting in oversampling of the footprints at 1-s intervals. The oversampling of the footprint permits approximate collocation of time-averaged radiometer and radar footprints. There is an uncertainty of a few microseconds in the time delay between command and operation of the radar switches, which places a lower limit of about 1 km on the altitude at which the radar can reliably operate.

5. References and Related Publications

Wilson, W.J., S.H. Yueh, S.J. Dinardo, S. Chazanoff, F.K. Li, and Y. Rahmat-Samii (2001): Passive Active L- and S-band (PALS) microwave sensor for ocean salinity and soil moisture measurements, IEEE Trans. Geosci. Rem. Sens. 39, 1039-1048.

6. Document Information

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document.

AMSR-E Advanced Microwave Scanning Radiometer - Earth Observing System
IR Infrared
PALS Passive and Active L- and S-band
RFI Radio-Frequency Interference
SMEX Soil Moisture Experiment
TB Brightness Temperature
UTM Universal Transverse Mercator

Document Creation Date

August 2003

Document URL

http://nsidc.org/data/docs/daac/nsidc0183_smex_pals.gd.html