CLPX-Ground: Ground-based L and Ku Band Polarimetric Scatterometry
Summary
This data set includes ground-based radar observations carried out at the Fraser Experimental Forest Headquarters, Colorado, USA (39.95 N, 105.9 W), between 17-26 February and 26-30 March 2003. Truck-mounted L- and Ku-band scatterometers were used to collect fully polarimetric backscattering coefficients of snow. The calibrated radar systems measured the amplitude and phase of backscattered signal over a relatively wide bandwidth at L-band (1.1-1.4 GHz) and Ku-band (15.25-15.75 GHz). Backscatter measurements of an open snow pack were collected at three different incidence angles (20, 35, and 50 degrees) several times a day. This data set is part of the NASA Cold Land Processes Field Experiment (CLPX).
The NASA CLPX is a multi-sensor, multi-scale experiment that focuses on extending a local-scale understanding of water fluxes, storage, and transformations to regional and global scales. Within a framework of nested study areas in the central Rocky Mountains of the western United States, ranging from 1-ha to 160,000 km2, intensive ground, airborne, and spaceborne observations are collected. Data collection focuses on two seasons: mid-winter, when conditions are generally frozen and dry, and early spring, a transitional period when both frozen and thawed, dry and wet conditions are widespread.
Citing These Data
Sarabandi, Kamal. 2003. CLPX-Ground: Ground-based L and Ku band polarimetric scatterometry. Boulder, CO: National Snow and Ice Data Center. Digital Media.
Overview Table
| Category | Description |
|---|---|
| Data format | Tab-delimited ASCII, and two Microsoft Excel worksheets |
| Spatial coverage and resolution | Spatial coverage: 39.95 N, 105.9 W Spatial resolution: For L-band radar ~2.5m x 3.0m (at 35 degrees) for Ku-band radar: ~0.6m x 0.6m |
| Temporal coverage and resolution | 17-26 February and 26-30 March 2003 |
| File size | 13.8 MB total |
| Parameter(s) | polarimetric radar backscattering coefficients |
| Procedures for obtaining data | Data are available via FTP. |
Table of Contents
1. Contacts
2. Detailed Data Description
3. Data Access
4. Data Acquisition
5. References and Related Publications
6. Document Information
1. Contacts
Investigator(s) Name and Title
Kamal Sarabandi
University of Michigan Radiation Laboratory
1301 Beal Avenue
Ann Arbor, MI 48109-2122
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
2. Detailed Data Description
This data set consists of fully polarimetric backscattering coefficients of snow, collected with truck-mounted L- and Ku-band scatterometers. The calibrated radar systems were used to measure the amplitude and phase of backscattered signal over a relatively wide bandwidth at L-band (1.1-1.4 GHz) and Ku-band (15.25-15.75 GHz). Backscatter measurements of an open snow pack were collected at three different incidence angles (20, 35 and 50 degrees), several times a day. Radar data were collected over an open snowpack at approximately 39.95 N, 105.9 W. The spatial resolution of these data was ~2.5 m x 3.0 m (at 35 degrees) for L-band radar and ~0.6 m x 0.6 m for Ku-band radar.
Despite the extreme complexity of typical snowpacks, there is a growing interest in and need to characterize the physical parameters of snow from active and passive microwave sensors (radars and radiometers). There is also a need to investigate the influence of water content within a snowpack on these parameters throughout diurnal cycles of freezing and thawing. Traditional scatterometers use only a single polarization for transmitting and receiving, but polarimetric scatterometers provide the full polarimetric response of a target, which contains valuable information about the structure and composition of the target. Two frequencies were chosen for this study so that the responses obtained were influenced by different parts of the snowpack. At L-band, where the wavelength (~20cm) is long enough to allow penetration all the way through to the bottom of the snowpack, the scattered wave is expected to have a significant if not dominant contribution from the underlying ground. At Ku-band (and to a greater extent at millimeter-wave frequencies), the roughness and the effective dielectric constant of the snow top can have a major influence, and the total penetration depth will probably be relatively shallow.
Format
Data files are in ASCII format. Two Microsoft Excel files provide a summary listing of results (one for IOP3 and one for IOP4).
Each data file contains:
- the Mueller Matrix (described in Sarabandi, 1992) averaged over the number of spatial samples (typically between 20 and 60 independent spatial samples)
- the Mueller Matrix averaged over both frequency and spatial samples (351 frequency points are kept in this averaging)
- the Mueller Matrix parameters (radar backscattering coefficient [in dB] for all four polarizations, degree of correlation [alpha], polarized phase difference [Zeta,in degrees], and the "cross-pol/co-pol" ratio [in dB])
File Naming Convention
Data files are named with the band name (Ku or L), the date, and the time of measurement. For example, the file called "Ku02191349.mdt" contains data collected by the Ku-band radar, on 19 Feb (0219) 2003. Data collection began at 13:49 (1:49 pm) local time.
File Size
Data files range in size from 140 to 142 KB. The MS Excel summary files are 236 and 406 KB.
Spatial Coverage
Measurements were taken at the Fraser Experimental Forest Headquarters, Colorado, USA (39.95 N, 105.9 W). This area is known as the CLPX Local-Scale Observation Site (LSOS).
Spatial Resolution
Spatial resolution for the L-band radar was ~2.5m x 3.0m (at 35 degrees); for the Ku-band radar resolution was ~0.6m x 0.6m.
Temporal Coverage
Measurements were taken during 17-26 February and 26-30 March 2003, between 9 am and 6 pm local time.
Parameter or Variable
Parameters presented in this data set are fully polarimetric backscattering coefficients of snow.
Sample Data Record
The following is a sample of the header information and the first line of data in file "Ku02191349.mdt".
Time of Measurement: 1:49:00 PM, Date: Wednesday, February 19, 2003 Frequency Band: Ku Center Frequency, Start Frequency, and Stop Frequency (GHz) are: 15.50 15.25 15.75 Number frequency points: 401 Number of frequency points saved: 401 Number of spatial samples (positions): 100 Comments on the Target/Experiment: 25 degrees outside, sunny Height Above Ground from H-frame(m), and Incidence Angle From Vertical (deg): 11.3 20 Time of Gating: 3:11:14 PM, Date: Friday, April 25, 2003 Gate Start and Stop in nanosec. are: 385.1 390.2 Final Product File Name: Ku02191349.mdt Target Data File (gated) used: Ku02191349.gdt Sphere Data File (gated) used: Ku02191544.gcl Background Data File (gated) used: Ku02191554.gbk -------------------------------------------------------------------------------------- Mueller Matrix averaged over Spatial Samples Freq No. 25 1.931087E-02 8.549867E-04 -2.551991E-03 -3.303421E-04 1.666165E-03 8.444589E-03 -1.237152E-03 -9.992628E-04 -4.504739E-03 -3.474953E-03 9.894152E-03 3.939702E-03 etc.... Mueller Matrix averaged over Both Frequency and Spatial Samples 7.858613E-03 7.297072E-04 1.090616E-05 -8.492468E-05 7.61836E-04 6.813205E-03 -2.268498E-04 -9.295072E-05 -3.783498E-04 -1.173277E-04 5.346445E-03 1.335911E-03 -1.485124E-04 -2.276916E-04 -1.093896E-03 5.027399E-03 -------------------------------------------------------------------- sig_vv sig_hh sig_vh sig_hv alpha_c zeta_c xpol/copol -10.05457 -10.67452 -20.37667 -20.18954 0.7280458 13.18243 -9.928607
Microsoft Excel Summary Files
IOP3_UM_Radar_Measurements.xls has three worksheets. Worksheet 1 has three subsections:
- Plots of co- and cross-polarized backscattering coefficients as a function of incidence angle for each measurement session in IOP3. These are not new data products, but they are graphical representations of the data in the *mdt files.
- Plots of degree of correlation and polarized phase difference (degrees) as a function of incidence angle. Two new products are derived from the following two equations:
- Other plots showing how the backscattering coefficient changes over time in vv and hh polarizations for Ku and L bands at the three different incidence angles (20, 35, 50).
Worksheet 2 provides a summary spreadsheet of all the Mueller Matrices parameters (found at the end of each *.mdt file) from IOP3. This includes the data from which the 'other plots' in Worksheet 1 were created.
Worksheet 3 repeats some of the data for the 'other plots' on Worksheet 1 but also compares it to 'real' data.
IOP4_UM_Radar_Measurements.xls has two worksheets. Worksheet 1 has three subsections:
- Plots of co- and cross-polarized backscattering coefficients as a function of incidence angle and time for each measurement session in IOP4. These are not new data products, but they are graphical representations of the data in the *mdt files.
- Plots of degree of correlation and polarized phase difference (degrees) as a function of incidence angle. Two new products are derived from the following two equations:
- Other plots showing how the backscattering coefficient changes over time in vv and hh polarizations for Ku and L bands at the three different incidence angles (20, 35, 50).
Worksheet 2 provides a summary spreadsheet of all the Mueller Matrices parameters (found at the end of each *.mdt file) from IOP4. This includes the data from which the 'other plots' in Worksheet 1 were created.
3. Data Access
Data Access
Data are available via FTP at ftp://sidads.colorado.edu/pub/DATASETS/CLP/data/ground_data/nsidc0166_lsos_scatterometer/
Related Data Collections
4. Data Acquisition
Site specifications at the Fraser Experimental Forest Headquarters, Colorado, USA, are:
- Open snowpack of approximately 200 m2
- Snow Conditions: dry during IOP3, wet and melting during IOP4 (limited)
- Ground Conditions: rough surface.
The data were collected with the following radars:
L-band polarimetric scatterometer
Center Frequency: 1.25 GHz
Bandwidth: 300 MHz
Ku-band polarimetric scatterometer
Center Frequency: 15.50 GHz
Bandwidth: 500 MHz
3 incidence angles: 20, 35 and 50 degrees
4 linear polarizations: VV, VH, HV, HH
5. References and Related Publications
Tassoudji, M. A., K. Sarabandi and F.T. Ulaby. 1989. Design consideration and implementation of the LCX polarimetric scatterometer (POLARSCAT). Radiation Laboratory Report No 022486-T-2, The University of Michigan, June.
Kendra, J. R.. 1995. Microwave Remote Sensing of Snow: An Empirical/Theoretical Scattering Model for Dense Random Media. Ph.D. thesis, Univ. of Michigan, Sep.
Ulaby, F.T., C. Elachi. 1990. Radar Polarimetry for Geoscience Applications. Dedham MA: Artech House, Inc.
K. Sarabandi. 1992. Derivation of phase statistics from the Mueller matrix. Radio Sci., Vol. 27, Sept.-Oct.
Sarabandi, K. and F.T. Ulaby. 1990. A convenient technique for polarimetric calibration of single-antenna radar systems. IEEE Trans. Geosci. Remote Sensing, Vol. 28, pp 1022-1033.
Sarabandi, K., F.T. Ulaby, and M.A. Tassoudji. 1989. Calibration of polarimetric radar systems with good polarization isolation. IEEE Trans. Geosci. Remote Sens., Sep.
Sarabandi, K., Y. Oh, and F.T. Ulaby. 1992. Measurement and calibration of differential Mueller matrix of distributed targets. IEEE Trans. Antennas Propagat., Vol. 40, pp 1524-1532.
Ulaby, F.T., R.K. Moore, and A.D. Fung. 1986.Microwave Remote Sensing: Active and Passive. Vol 1, Dedham, MA: Artech House, Inc.
6. Document Information
List of Acronyms
CLPX = NASA Cold Land Processes Field Experiment
IOP = Intensive Observation Period
ISA = Intensive Study Area
LRSA = Large Regional Study Area
LSOS = Local Scale Observation Site
MSA = Meso-cell Study Area
Document Creation Date
5 September 2003
Document Revision Date
Document URL
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