BYU High Resolution Images of Seasat Sigma0 Measurements (D. Long)

Summary:

The Seasat scatterometer (SASS) provided normalized radar cross section (sigma0) measurements of the Earth's surface. While originally designed for wind observation, scatterometer sigma0 measurements have proven useful in a variety of land and ice studies. To aid in the application of these measurements, Brigham Young University prepared this dataset consisting of enhanced resolution images generated from SASS sigma0 measurements.

This data set consists of enhanced resolution images generated from Seasat sigma0 measurements.

Table of Contents:

1. Data Set Overview:

Data Set Identification:

BYU High Resolution Images of Seasat Sigma0 Measurements (D. Long).
JPL PO.DAAC Product 175

Data Set Introduction:

This data set contains images from 16 regions around the globe. Images are made from the Seasat Scatterometer Geophysical Record data files and processed using the BYU SIRF algorithm. To produce the highest possible spatial resolution as well as to ensure full coverage over the images, multiple orbit passes are combined.

Objective/Purpose:

The first wind scatterometer, the Ku-band Seasat Scatterometer (SASS), demonstrated the capability of a spaceborne scatterometer to measure ocean winds. SASS also demonstrated the utility of scatterometer data in land and ice studies. This 1978 data set provides a baseline for studies of global change.

Summary of Parameters:

Each data file contains one image and represents a unique combination of:
  • polarization
  • geographical region
  • time span
  • image type
  • reconstruction technique
Landmasked versions of some files are often available as well.

Discussion:

SASS made approximately 50 km resolution sigma0 measurements over an irregularly spaced grid. Orbit passes of a given point on the Earth occured at nearly the same time of day.

Capable of dual-polarization operation over a single 500 km wide swath, SASS normally operated in V-pol, dual-sided swath mode over the ocean. Unlike later scatterometers, its operating mode changed very frequently over land. Only a limited amount of H-pol data was collected over land and ice during the mission. The limited spatial coverage necessitates long imaging time periods, yet there are still frequent gaps in the image coverage.

Images of both V and H pol backscatter are produced. Because SASS made measurements of sigma0 over a range of incidence angles, a simple scheme was used to model the incidence angle variation: a linear model relating sigma-0 and incidence angle is assumed where

sigma-0(db) = A + B (theta - 40)
where A is the "incidence angle normalized sigma-0" at 40 deg incidence in dB, B is the effective incidence slope of sigma-0 versus incidence angle in dB/deg, and theta is the incidence angle of the observation. While SASS collected backscatter measurements at near-nadir incidence angles, only measurements with incidence angle greater than 15 deg were used in making image products of A and B. Images of A and B, as well as ancillary images, are made at both the nominal sensor resolution and at enhanced resolution. The effective resolution of the enhanced resolution images vary depending on region and sampling conditions.

Related Data Sets:

Seasat Data Products
  • Seasat Scatterometer GDR
    JPL PO.DAAC Product 22
  • Seasat Altimeter GDR
    JPL PO.DAAC Product 19
  • Seasat Scatterometer Global 50km sigma-0 data '78 (Wentz)
    JPL PO.DAAC Product 31
  • Seasat Scatterometer Global Dealiased Wind Vectors '78 (Wentz et al.)
    JPL PO.DAAC Product 29
  • Seasat Scatterometer Global Gridded Monthly Surface Wind Stress (Chelton)
    JPL PO.DAAC Product 8
The Scatterometry Climate Record Pathfinder (SCP), http://scp.byu.edu, at Brigham Young University is the source of this and other data sets available from PO.DAAC:
  • BYU Daily Browse Images of QuikSCAT Sigma-0 Measurements (D. Long)
    JPL PO.DAAC Product 121
  • BYU High Resolution Images of QuikSCAT Sigma-0 Measurements (D. Long)
    JPL PO.DAAC Product 122, available soon
  • BYU QuikSCAT-Derived Antarctic and Arctic Sea-Ice Extent Maps (D. Long)
    JPL PO.DAAC Product 123, available soon
  • BYU NSCAT-Derived Sea-Ice Extent (D. Long)
    JPL PO.DAAC Product 124, available soon
  • BYU High Resolution Images of NSCAT Sigma0 Measurements (D. Long)
    JPL PO.DAAC Product 176, available soon
  • BYU High Resolution Images of ERS Sigma0 Measurements (D. Long)
    JPL PO.DAAC Product 177, available soon
  • BYU ERS-Derived Antarctic and Arctic Sea Ice Extent Maps (D. Long)
    JPL PO.DAAC Product 179, available soon

2. Investigator(s):

Investigator:Dr. David G. Long
Title:Director, BYU Center for Remote Sensing
Professor, Department of Electrical & Computer Engineering
Address: 459 Clyde Building
Brigham Young University
Provo, UT 84602
Email: long@ee.byu.edu
Fax:(801)378-6586

3. Theory of Measurements:

The Seasat-A Satellite Scatterometer (SASS) was an active microwave sensor operating at a frequency of 14.6 GHz (wavelength = 2.1 cm). It was designed to measure the normalized radar cross-section (NRCS) backscatter (also termed sigma0) of the surface. Over the ocean, the backscatter is due to Bragg scattering of microwaves from centimeter length capillary ocean waves which is related to the wind. The scattering is greater for higher wind speeds and is anisotropic; thus sigma0 measurements from multiple azimuth angles can be used to estimate the near-surface vector wind. Over land, the backscatter is related to the surface roughness and dielectric properties as well as volume scattering from vegetation and snow cover. Over ice, the backscatter is very sensitive to melting and brine inclusions. It is also sensitive to the internal structure of the ice via volume scattering.

4. Equipment:

Sensor/Instrument Description:

Collection Environment:

Seasat satellite

Source/Platform:

Seasat was launched June 26, 1978 on-board an Atlas-Agena rocket from Vandenberg Air Force Base, California. On October 10, 1978, the satellite suffered a massive short circuit in its electrical system and stopped functioning.

The satellite orbit is near-circular, with an inclination of 108 deg, a period of 101 min, and an altitude of a 790km. During its period of operation, Seasat circled the Earth 14 times daily, covering 95 percent of the global ocean area every 36 hours, and completing 1503 revolutions of the Earth.

SEASAT Configuration

Source/Platform Mission Objectives:

"The objective of the [Seasat-A Satellite Scatterometer] was to provide a closely spaced grid measurement (~50 km) of ocean-surface wind speed and direction in the range of 4 to >= 26 m/s, accurate to ± 2 m/s or 10 percent (whichever is greater) in magnitude and ± 20 deg in direction" [Boggs, 1982].

Key Variables:

"The physical 'observable' measured by the scatterometer is the NRCS backscatter coefficient sigma-0" [Boggs, 1982].

Principles of Operation:

"Four dual-polarized (vertical (V) and horizontal (H) polarizations) fan-beam antennas were aligned so that they pointed 45 and 135 deg relative to the spacecraft flight direction (in the orbit plane) to produce an X-shaped illumination pattern on the Earth. In this way a given surface location was first viewed by a forward antenna, and then viewed, somewhere between a few seconds and about three minutes later -- depending on the location's cross-track distance from the subsatellite track -- near-orthogonally by an aft antenna. Thus, sigma-0 measurements of the same region were provided at two azimuthal angles separated by approximately 90 deg."

"The illumination pattern for each antenna was active for 1.89-s measurement periods. The 1.89-s measurement interval was repeated continually and contiguously, but a different antenna or polarization was activated for each consecutive sampling period. Each of eight possible SASS science operational modes was associated with a different prescribed antenna/polarization sequence ordered .... All modes were characterized by an antenna switching-cycle period of 7.56 s, during which four antenna-beam/polarization combinations were cycled through. This timing was to provide sigma-0 measurements spaced approximately 50km apart (footprint area center-to-center distance) in the along-track direction"

"Fifteen Doppler filters were used to electronically subdivide each full antenna footprint into 15 measurement resolution "Doppler" cells of approximate dimension 20 km (cross-beam) by 50 km (along-beam). The intersection of the antenna-beam pattern and Doppler lines determined the resolution cell size, orientation, and location on the Earth.... The instantaneous-field-of-view (IFOV) cell boundaries were determined by the Doppler filter noise bandwidth and the antenna 3-dB beamwidth (.5 deg) in the narrow-beam dimension. [The integrated cell is the area swept out by a sequence of 61 overlapping IFOV cells generated over the course of a 1.89-s measurement period.] The surface area of this final integrated Doppler resolution cell is greater than the instantaneous illuminated region because the satellite moved (about 12.5-km ground-track distance) during the measurement period. Each of these integrated Doppler cells is a SASS footprint, and has one sigma-0 backscatter measurement value associated with it" [Boggs, 1982].

Scatterometer Ground Pattern and Swath

Sensor/Instrument Measurement Geometry:

"Twelve of the Doppler filters ...generated the two primary sigma-0 measurement swath strips that lie on either side of the subtrack (for two-sided modes). These two swaths typically extend from about 200 to 950km in cross-track distance from nadir (for two-sided modes) with incidence angles ranging from 22 to 67 deg. The remaining three Doppler filters yielded resolution cells with incidence angles near nadir -- at about 0, 4, and 8 deg, respectively -- that generated two (for two sided modes) 90-km-wide overlapping nadir-region strips" [Boggs, 1982].

Manufacturer of Sensor/Instrument:

NASA Langley Research Center
Hampton, VA 23681

Calibration:

Specifications:

...

Tolerance:

...

Frequency of Calibration:

"After every group of 124 frames -- about 4 min of data -- science data is interrupted by the presence of 4 calibration frames in the data stream." [Boggs, 1982]

Other Calibration Information:

"The nominal sequence of 4 calibration frames followed by 124 science frames was interrupted only by (1) the appearance of an uncorrected time regression ..., (2) missing data frames (i.e., a time gap in the data stream), and (3) a scatterometer mode change" [Boggs, 1982].

Extensive post-launch calibration efforts have demonstrated the calibration accuracy of the measurements [Long and Skouon].

5. Data Acquisition Methods:

Data are transmitted from the satellite in three separate streams: a 25-kbps real-time stream containing instrument data from ALT, SASS, SMMR, and VIRR and all engineering subsystem data, an 800-kbps playback stream of recorded real-time data, and a 20-MHz analog SAR instrument data stream.

Spacecraft data are received and recorded by tracking stations of the Spaceflight Tracking Data Network (STDN) and transmitted to the Goddard Space Flight Center (GSFC). There, data are sorted, merged, time tagged, and recorded on magnetic tape, which is then shipped to the Instrument Data Processing System (IDPS) at JPL.

The data package received from GSFC consists of the Sensor (non-SAR) and engineering data as well as attitude and orbit determination data. These data are decommutated, organized by major frame, and converted from data numbers to engineering units. Footprint locations are calculated, and data are then formatted into archival-quality SDR (Sensor Data Record) tapes suitable as input for engineering assessment and geophysical processing.

6. Observations:

Data Notes:

No additional notes.

Field Notes:

No additional notes.

7. Data Description:

Spatial Characteristics:

Spatial Coverage:

Alaska Greenland North America North America Central America Antarctica South America South America Europe Northern Africa Northern Africa Southern Africa Siberia Bering Sea Bering Sea China and Japan Southern Asia Southern Asia Arctic Indonesia Indonesia Australia and New Zealand
The 16 regions of this data set are:
Alaska, Antarctic, Arctic, Australia, Bering Sea, Central America, China and Japan, Europe, Greenland, Indonesia, North America, North Africa, Siberia, South Africa, South America, South Asia

Spatial Coverage Map:

For information regarding longitude crossing times, refer to "SEASAT Node Tables and Osculating Orbital Elements", [Klose, 1979].

The absolute value of a pixel in a count image indicates the number of sigma-0 measurements that hit the pixel during the imaging interval. Zero indicates no data.

Spatial Resolution:

Each file's reconstruction technique determines its resolution.
SIR, average files: 4.45 km pixel grid
Gridded files: 22.25 km pixel grid
A field in the header identifies the resolution.

Projection:

Each file's geographical region determines its projection.
Antarctic, Arctic files: polar stereographic projection
All others: Lambert Equal Area projection
A field in the header identifies the projection.

Grid Description:

Two auxiliary files for each region at each spatial resolution (i.e. 4.45 km/pix for SIR and average files, 22.25 for gridded) contain the longitude and latitude for the center of each pixel. The files are in the same format as the product but have a latitude or a longitude value instead of a sigma0 value stored in the image. The naming scheme for these auxiliary files is:
sas-T-reg.rcn
Timage type x = longitude, y = latitude
regregion Ala = Alaska, Ant = Antarctica, ...
rcn reconstruction technique sir = SIR, grd = gridded

Two other types of auxiliary files for each region at each spatial resolution contain topography and land mask information. The naming scheme for these files is:

sas-reg.rcn.info
regregion Ala = Alaska, Ant = Antarctica, ...
rcn reconstruction technique sir = SIR, grd = gridded
infotype topo = topography, lmask = land mask

Temporal Characteristics:

Temporal Coverage:

7 July 1978 - 10 October 1978

Temporal Coverage Map:

Not available.

Temporal Resolution:

Seasat's limited spatial coverage necessitates long imaging time, ranging from 12 to 48 days.

Data Characteristics:

Parameter/Variable:

Each data file contains one image and represents a unique combination of parameters, which is reflected in the naming scheme.
sasp-T-regyy-dd1-dd2.rcn[.lmsk]
ppolarization
h
horizontal
v
vertical
Timage type
a
sigma0 average, the normalized sigma0 at a 40° incidence angle
V
sigma0 standard deviation
E
sigma0 error
b
sigma0 slope, sigma0 vs. incidence angle
J
average incidence angle
I
incidence angle standard deviation
C
count, the number of measurements
p
pixel time
reg geographical
region -
see Spatial
Coverage

above
Ala Alaska
Ant Antarctic
Arc Arctic
Aus Australia
Ber Bering Sea
CAm Central America
ChJ China and Japan     Eur Europe
Grn Greenland
Ind Indonesia
NAm North America
NAf North Africa
SAf South Africa
SAm South America
SAs South Asia
Sib Siberia
yy two-digit year, always 78
dd1 three-digit day of year, start of imaging
dd2 three-digit day of year, end of imaging
rcn reconstruction
technique
sir
SIR or SIRF. The Data Manipulations section describes SIR processing generally then specifically for SASS.
ave
average, the first iteration of the SIR algorithm, less enhanced but less noisy (see Processing Steps)
grd
gridded, non-enhanced on a coarser grid
lmsk land mask. Optional. If present, image is land masked.

The Grid Description section describes the naming scheme and the meanings of the auxiliary files.

Variable Description/Definition:

See the previous section

Unit of Measurement:

This depends upon the image type.
a
sigma0 average: dB
V
sigma0 standard deviation: dB
E
sigma0 error: dB
b
sigma0 slope: dB/deg
J
average incidence angle: deg
I
incidence angle standard deviation: deg
C
count: unitless
p
pixel time

Data Source:

SASS data was obtained from the SASS GDR data set. No recalibration has been applied.

Data Range:

...

Sample Data Record:

Each file contains 1 image, which can be visualized using the software described below, such as the modified version of xv.

Each file also has header information. The program xv printed the following sample output as it displayed the file sasv-a-Ala78-188-233.sir.lmsk:

    SIR file header: 'sasv-a-Ala78-188-233.sir.lmsk'
      Title:   'SIRF image of alaska'
      Sensor:  'SASS'
      Type:    'A image  (sasv-a-Ala78-188-233.sir)'
      Tag:     '(c) 1999 BYU MERS Laboratory'
      Creator: 'BYU MERS:sass_meta_sirf v1.0 Ai= -8.40 Bi=-0.140 Bw=30 It=50'
      Created: '01:39:18 03/19/01'
      Size: 810 x 630    Total:510300  Offset: -33  Scale: 1000
      Year: 1978  JD range: 188-233  Region Number: 203  Type: 1  Form: 2
      Polarization: 2  Frequency: 14.000000 MHz
      Datatype: 2  Headers: 1  Ver:30
      Nodata: -33.000000   Vmin: -32.000000  Vmax: 0.000000
      Lambert form: (local radius)
       Center point:      -155.000000 , 61.500000
       Lon, Lat scale:    4.450000 , 4.450000 (km/pix)
       Lower-Left Corner: -1800.000000 , -1300.000000
      Image Min, Max: -32.000000 , 0.000000

    Greyscale conversion range:  Min: -32.000000, Max:0.000000
    

8. Data Organization:

Data Granularity:

The basic granule is one data file. Each file has a unique combination of polarization, region, image type, time span, reconstruction technique, and land mask.

The EOSDIS Glossary describes data granularity generally as it applies to the IMS.

Data Format:

The BYU-MERS SIR image format was developed by the Brigham Young University (BYU) Microwave Earth Remote Sensing (MERS) laboratory to store a variety of image types along with the information required to Earth-locate the image pixels.

A SIR format file consists of one or more 512-byte headers followed by the image data and additional zero padding to insure that the file is a multiple of 512 bytes long. The file header record contains all of the information required to read the remainder of the file and the map projection information required to map pixels to lat/lon on the Earth surface. The image pixel values generally represent floating point values and may be stored in one of three ways. The primary way is as 2 byte integers (with the high order byte first), though the pixels may be stored as single bytes or IEEE floating point values. Scale factors are stored in the header to convert the integer or byte pixel values to native floating point units.

The image is stored in row-scanned (left to right) order from the lower left corner (the origin of the image) up through the upper right corner. By default, the location of a pixel is identified with its lower-left corner. The origin pixel (1,1) is the lower left corner of the image. The array index n of the (i,j)th pixel where i is horizontal and j is vertical is given by

n = (j - 1) × Nx + i
where Nx is the horizontal dimension of the image. The last pixel stored in the file is at (Nx, Ny).

The sir file header contains various numerical values and strings which describe the image contents. For example, the value for a no-data flag is set in the header as well as a nominal display range and the minimum and maximum representable value. Optional secondary header records (512 bytes) can be used to store additional, non-standard information.

The standard SIR file format supports a variety of image projections including:

  1. Rectangular array (no projection)
  2. Rectangular lat/lon array
  3. Two different types of Lambert equal-area projections which can be used in either non-polar or polar projections
  4. Polar stereographic projections
  5. EASE grid polar projection with various resolutions
  6. EASE global projection with various resolutions

Any of the programs described in Software below decodes SIR headers.

9. Data Manipulations:

Formulae:

Derivation Techniques and Algorithms:

In general, sir data files are generated using the scatterometer image reconstruction (SIR) resolution enhancement algorithm or one of its variants for radiometer processing. The multivariate SIR algorithm is a non-linear resolution enhancement algorithm based on modified algebraic reconstruction and maximum entropy techniques [Long, Hardin, and Whiting, 1993]. The singlevariate SIR algorithm was developed originally for radiometers [Long and Daum, 1997] but also used for SeaWinds [Early and Long, 2001]. The SIR w/filtering (SIRF) algorithm has been successfully applied to SASS and NSCAT measurements to study tropical vegetation and glacial ice (e.g. Long and Drinkwater, 1999). Variants of SIR have been successfully applied to the ERS-1/2 scatterometer and various radiometers (SSM/I and SMMR). (SIRF is used for SASS, NSCAT, and SeaWinds slice data processing. SIR is used for ERS-1/2 and SeaWinds egg data. The modified median filter [SIRF] is not used with ERS-1/2 data and SeaWinds egg data.)

For scatterometers, the multivariate form of the SIR algorithm models the dependence of sigma0 on incidence angle as sigma0 (in dB) = A + B * (Inc Ang - 40 deg) over the incidence angle range of 15 to 60 deg. The output of the SIR algorithm is images of the A and B coefficients. See the Data Characteristics section.

A represents the "incidence angle normalized sigma0" (effectively the sigma0 value at 40 deg incidence angle). The units of A are dB. Typically, +2 < A < -45 dB. However, in the SIR images A is typically clipped to a minimum -32 dB with values of A < -32 used to indicate 'no data'.

B describes the incidence angle dependence of sigma0 and has units of dB/deg. At Ku-band the global average of B is approximately -0.13 dB/deg. Typically, -0.2 < B < -0.1. B is clipped to a minimum value of -3 dB/deg. This value is used to denote 'no data' as well.

Single variable SIR or SIRF algorithms are used for radiometers and produce only an A (in this case, the brightness temperature) image. Typically, this can range from 165 to 320. Single variable SIR and SIRF algorithms are used for SeaWinds egg and slice images, respectively. In both cases the A images are at the nominal measurement incidence angle for the sensor and in the sensor measurement units.

Data Processing Sequence:

Processing Steps:

Enhanced resolution images made from SASS data use the Scatterometer Image Reconstruction with Filtering (SIRF) algorithm. This version of the algorithm incoporates a median filter and a simplified spatial response function in which the spatial response is assumed to be 1 over the footprint and 0 elsewhere. In the processing, a linear model relating sigma0 and incidence angle is assumed, i.e. sigma0(db) = A + B (theta - 40) where A is the "incidence angle normalized sigma0" at 40 deg incidence in dB, B is the effective incidence slope of sigma0 versus incidence angle in dB/deg, and theta is the incidence angle of the observation. The SIR algorithm makes images of A and B on a 4.5 km pixel grid. The effective resolution varies depending on region and sampling conditions. Multiple passes of the spacecraft are combined to produce a higher spatial resolution (at a cost of reduced temporal resolution) and fill in coverage gaps between the individual measurement footprints. SASS measurement footprints were not contiguous, had irregular six-sided shapes, and varied in size depending on beam and location on the earth.

SIRF is an interative algorithm, terminated after 50 iterations in this processing.

Processing Changes:

...

Calculations:

Special Corrections/Adjustments:

SASS data was obtained from the SASS GDR data set. No recalibration has been applied.

Calculated Variables:

...

Graphs and Plots:

None

10. Errors:

Sources of Error:

Capable of dual-pol operation over a single 500 km wide swath, SASS normally operated in V-pol, dual-sided swath mode over the ocean with the mode frequently switched over land, resulting in very little H-pol coverage during most of the abbrievated mission. SASS operated at 14.6 GHz. In combining the multiple passes, sigma0 is assumed to be independent of azimuth angle. While true for most areas, some azimuth dependence in sigma0 has been observed in Antarctic firn, presumably due to sastrugi or snow dunes.

The measurement accuracy of ° was affected primarily by communication noise, attitude pointing uncertainty, instrument processing (e.g., quantization errors and gain uncertainty), and various bias errors. Bias error are in general deterministic and, depending upon the existence of adequate comparison data, are removable. The remaining errors, which are random in nature and not removable, limit the ultimate accuracy of scattering coefficient measuremnts. [Boggs, 1982]

Quality Assessment:

Data Validation by Source:

...

Confidence Level/Accuracy Judgement:

...

Measurement Error for Parameters:

...

Additional Quality Assessments:

...

Data Verification by Data Center:

...

11. Notes:

Limitations of the Data:

The relatively short 3-month data set restricts the range of applications.

Known Problems with the Data:

...

Usage Guidance:

...

Any Other Relevant Information about the Study:

...

12. Application of the Data Set:

13. Future Modifications and Plans:

There are no future modifications or plans at this time.

14. Software:

Software Description:

Sample read and display software for SIR files are available in C, FORTRAN, IDL/PV-WAVE, and MATLAB. These programs can be easily modified to meet the requirements of individual users.
LanguageProgram NameDescription
C csir_dump.cdump SIR file to text output
csir_dump_small.c
csirexample.c read SIR file, print values of corner pixels
sir_ez_example.c
sir2bmp.cconvert SIR file to BMP
sir2byte.cconvert SIR file to raw, unsigned byte file
sir2gif.cconvert SIR file to GIF
sir2gif_ez.c
Fortran fsir_dump.fdump SIR file to text file
fsir_dump_small.f
fsir_locmap.fread SIR file, create latitude and longitude maps like the auxiliary files
fsir_locmap_EZ.f
fsirexample.f read SIR file, create an unsigned byte file
fsirexample_EZ.f
sir2byte.f
sirmask.fmask one SIR file over another to create masked SIR file
IDLxsir_idl.pro load SIR file, save to file, display image, do forward/inverse transforms
PV-WAVE xsir.pro, xsir_pvwave.pro load SIR file, save to file, display image, do forward/inverse transforms
MATLABloadsir.m, writesir.m, showimage.m, ... load SIR file, save to file, display image, do forward/inverse transforms
IDL is made by Research Systems, Inc.
PV-WAVE is made by Visual Numerics, Inc.
MATLAB is made by The MathWorks, Inc.
All are copyrighted software tools for numerical analysis and visualization.

Software Access:

The latest versions of the sample read and display software can be obtained via anonymous FTP from ftp://ftp.scp.byu.edu/pub/software/lang, where lang = "c", "f", "idl", or "matlab". JPL PO.DAAC also maintains a copy at ftp://podaac.jpl.nasa.gov/allData/seasat/L3/byu_scp/sigma0enhanced/sw/.

The IDL and PV-WAVE programs reside in one directory due to the similarity between the languages. xsir_idl.pro, xsir.pro, and xsir_pvwave.pro call the same functions, though the file loadsir.pro must be modified for PV-WAVE.

15. Data Access:

Contact Information:

For general questions and comments regarding this dataset, please contact
email: podaac@podaac.jpl.nasa.gov
url: http://podaac.jpl.nasa.gov/dataset/SEASAT_BYU_L3_OW_SIGMA0_ENHANCED
Email is the preferred method of communication.

Dr. David Long of BYU is the source of this dataset. Please contact him with more detailed questions. See Investigator for contact information.

Data Center Identification:

Jet Propulsion Laboratory (JPL)
Physical Oceanography Archive Center (PO.DAAC)

Procedures for Obtaining Data:

This data set is currently available via anonymous FTP at ftp://podaac.jpl.nasa.gov/allData/seasat/L3/byu_scp/sigma0enhanced/.

This data set is publicized courtesy of the PO.DAAC at JPL..

Data Center Status/Plans:

None

16. Output Products and Availability:

This data set is made available at PO.DAAC on behalf of the BYU SCP: http://scp.byu.edu

17. References:

Boggs, D.H., 1982. "Seasat Geophysical Data Record (GDR) Users Handbook - Scatterometer", JPL Document D-129, Jet Propulsion Laboratory, Pasadena, CA.

Early, D.S. and D.G. Long, Feb 2001. "Image Reconstruction and Enhanced Resolution Imaging From Irregular Samples," IEEE Transactions on Geoscience and Remote Sensing, Vol. 39, No.2, pp. 291-302.

Klose, J.C., 1979. "Seasat Node Tables and Osculating Orbital Elements", JPL Internal Document 622-215, Jet Propulsion Laboratory, Pasadena, CA.

Long, D.G. and D. Daum, 1997. "Spatial Resolution Enhancement of SSM/I Data," IEEE Transactions on Geoscience and Remote Sensing, Vol. 36, pp. 407-417.

Long, D.G. and M.R. Drinkwater, 1999. "Cryosphere Applications of NSCAT Data," IEEE Transactions on Geoscience and Remote Sensing, Vol. 37, No. 3, pp. 1671-1684.

Long, D.G., P. Hardin, and P. Whiting, 1993. "Resolution Enhancement of Spaceborne Scatterometer Data," IEEE Transactions on Geoscience and Remote Sensing, Vol. 31, pp. 700-715.

Long, D.G. and G.B. Skouson, Mar 1995. "Calibration of Spaceborne Scatterometers Using Tropical Rainforests," IEEE Transactions on Geoscience and Remote Sensing, Vol. 34, No. 2, pp. 413-424.

18. Glossary of Terms:

See the EOSDIS Glossary for a more general listing of terms related to the Earth Observing System project.

19. List of Acronyms:

ALT: Seasat Radar Altimeter
EOS: Earth Observing System
EOSDIS: Earth Observing System Data and Information System
FTP: File Transfer Protocol
GDR: Geophysical Data Record
IDL: Interactive Data Language
JPL: Jet Propulsion Laboratory
NASA: National Aeronautics and Space Administration
NRCS: normalized radar cross-section
NSCAT: NASA Scatterometer
PO.DAAC : Physical Oceanography Distributed Active Archive Center
QuikSCAT: the NASA Quick Scatterometer spacecraft, or
QuikSCAT: usually refers to the SeaWinds instrument on the spacecraft
SAR: Synthetic Aperture Radar
SASS : Seasat Satellite Scatterometer
SDR: Sensor Data Record
SMMR : Scanning Multichannel Microwave Radiometer
SSM/I: Special Sensor Microwave/Imager
STDN : Spaceflight Tracking and Data Network
URL: Uniform Resource Locator
VIRR : Visual and Infrared Radiometer

20. Document Information:

Document Creation Date:

23 April 2002

Document Review Date:

23 April 2002

Document Revison Date:

8 December 2011

Document ID:

D-23179

Citation:

Document originally written by Richard Chen based heavily on information on the BYU SCP web site, http://scp.byu.edu.

Document Curator:

PO.DAAC Data Engineering Team
podaac@podaac.jpl.nasa.gov

Document URL:

ftp://podaac.jpl.nasa.gov/allData/seasat/L3/byu_scp/docs/dLongSass.html