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. 2003. SMEX02 Passive and Active L and S band System (PALS) Data. Boulder, CO: National Snow and Ice Data Center. Digital media.

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

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.

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

Service Interruption

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

Summary

Overview Table

Table of Contents

1. Contacts and Acknowledgments

2. Detailed Data Description

3. Data Access and Tools

4. Data Acquisition and Processing

25 June 2002 Files

27 June 2002 Files

1 July 2002

2 July 2002

5 July 2002

6 July 2002

7 July 2002

8 July 2002

5. References and Related Publications

6. Document Information

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