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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.
Sarabandi, K. 2003. CLPX-Ground: Ground-based L and Ku band polarimetric scatterometry. [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center.
|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 and HTTPS.|
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National Snow and Ice Data Center
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University of Colorado
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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.
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:
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.
Data files range in size from 140 to 142 KB. The MS Excel summary files are 236 and 406 KB.
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 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.
Measurements were taken during 17-26 February and 26-30 March 2003, between 9 am and 6 pm local time.
Parameters presented in this data set are fully polarimetric backscattering coefficients of snow.
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
IOP3_UM_Radar_Measurements.xls has three worksheets. Worksheet 1 has three subsections:
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:
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.
Site specifications at the Fraser Experimental Forest Headquarters, Colorado, USA, are:
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
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.
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.
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
5 September 2003