SEA-ICE EXTENT IMAGES & EDGE PRODUCTS Files are copyright 1999 by BYU. For each image time interval, a corresponding ASCII text file is included on this CD specifying the latitudes and longitudes of the ice edge. For details on the format of these files, see Sea-ice-extent.txt on this CD. Information on the image naming format, standard SIRF image regions and general documentation of the BYU-MERS "SIR" image format is given below. ************************************************************************** FILE NAMING FORMAT Standard SIR file name format: SENS-T-REGYR-DY1-DY2.RCN where SENS = Sensor (4 char): nscv = NSCAT V nsch = NSCAT H quev = QuikSCAT V - asc. and des. queh = QuikSCAT H - asc. and des. qaev = QuikSCAT V - ascending qaeh = QuikSCAT H - ascending qdev = QuikSCAT V - descending qdeh = QuikSCAT H - descending T = type (1 char) (header value for itype on left) 1 a = A image (sigma-0 in dB at 40 deg incidence) 2 b = B image (slope of sigma-0 in dB/deg) 4 c = C image (2nd order curvature of sigma-0 in dB/deg**2) 5 d = D image (3rd order curvature of sigma-0 in dB/deg**3) 21 E = Sigma-0 error image 8 C = counts or hits (measurements) per pixel 7 I = incidence angle standard deviation (in deg) 9 J = average incidence angle (in deg) 6 N = counts of negative sigma-0 values 11 p = pixel time estimate (in min from start of image interval) 12 S = counts of small sigma-0 values 22 V = Sigma-0 standard deviation image 16 W = mean wind speed image 30 x = longitude image 31 y = latitude image 17 Y = wind speed standard deviation image ?? X = misc. REG = Region (3 char) Here is a list of the standard regions and there corresponding numerical codes: (see below) Ant = (100) Antarctica Arc = (110) Artic Grn = (202) Greenland Ala = (203) Alaska CAm = (204) Central America NAm = (205) North America SAm = (206) South America NAf = (207) North Africa SAf = (208) South Africa Sib = (209) Siberia Eur = (210) Europe SAs = (211) South Asia ChJ = (212) China-Japan Ind = (213) Indonesia Aus = (214) Australia Ber = (256) Bering Sea Glb = (500) Globe YR = year (2 char) eg. - 96 or 97 DY1 = First Julian day of data used to make image (3 char) eg. - 001 or 267 DY2 = End Juilan day of data used in image (3 char) RCN = Reconstruction technique (3 char): sir = sir or sirf ave = ave image algorithm non = nonenhanced grd = gridded Special Extensions: ------------------- The following extensions may be added to the end of the filename to identify other image types: .lmsk = Land masked image .imsk = Ice masked image .omsk = Ocean masked image .dif = Difference image ******************************************************************** SIRF Standard regions: SIRF images are made over several standard regions identified by number, name, and a rectangular box in lat/long. Land images are typically produced in Lambert projection while Polar images are produced in Polar stereographic projection. A list of the standard image regions follows. Reg # LL-Lat LL-Long UR-Lat UR-Lon Reg. Name =============================================================== 100 -90.0 -180.0 -52.0 180.0 Antarctic 110 60.0 -180.0 90.0 180.0 Arctic 202 59.0 -74.0 84.5 -11.0 Greenland 203 50.0 -180.0 73.0 -130.0 Alaska 204 5.0 -115.0 30.0 -57.0 Cntrl-Amer 205 25.0 -135.0 65.0 -50.0 North-Amer 206 -58.0 -83.0 15.0 -32.0 South-Amer 207 2.0 -20.0 40.0 65.0 North-Afri 208 -38.0 5.0 10.0 53.0 South-Afri 209 50.0 60.0 75.0 180.0 Siberia 210 35.0 -12.0 72.0 65.0 Europe 211 5.0 60.0 30.0 130.0 South-Asia 212 25.0 60.0 55.0 150.0 Chin-Japan 213 -15.0 93.0 10.0 165.0 Indonesia 214 -48.0 110.0 -10.0 180.0 Australia ******************************************************************** Documentation of the BYU-MERS "SIR" image format The BYU-MERS "sir" image format was developed by the Brigham Young University (BYU) Microwave Earth Remote Sensing (MERS) research group to store images of the earth along with the information required to earth-locate the image pixels. A "sir" file consists of one or more 512 byte headers containing all the information required read the remainder of the file and the map projection information required to map pixels to lat/lon on the Earth surface. Pixel values are generally stored as 2 byte (high order byte first) integers though can be stored as bytes or IEEE floating point. The latter is not portable to all machines and so is not recommended. Scale factors to convert the integer or byte pixel values to native floating point units are stored in the file header. The origin of the images are in the lower left corner. The earth locaion of a pixels is identified with its lower-left corner. The standard sir format supports a variety of image projections including: 0. Rectangular array (no projection) 1. A rectangular lat/lon array 2. Two different types of Lambert equal-area projections which can be use in both non-polar and polar projections 3. Polar stereographic projections 4. EASE grid polar projection with various resolutions 5. EASE global projection with various resolutions In general, *.sir image data files have been generated using the scatterometer image reconstruction with filtering (SIRF) resolution enhancement algorithm or one of its variants for radiometer processing. The multivariate SIRF algorithm is a non-linear resolution enhancement algorithm based on modified algebraic reconstruction and maximum entropy techniques. The algorithm is described in detail in Long, D.G., P.J. Hardin, and P.T. Whiting, "Resolution Enhancement of Spaceborne Scatterometer Data," IEEE Trans. Geoscience Remote Sens., Vol. 31, No. 3, pp. 700-715, May 1993. The SIRF algorithm has been successfully applied to SASS and NSCAT measurements to study tropical vegetation and glacial ice. Variants of SIRF has been successfully applied to ERS-1 scatterometer and various radiometers (SSM/I and SMMR). For scatterometers, the multivariate form of the SIRF algorithm models the dependence of sigma-0 on incidence angle as sigma-0 (in dB) = A + B * (Inc Ang - 40 deg) over the incidence angle range of 15 to 60 deg. The output of the SIRF algorithm is images of the A and B coefficients. A represents the "incidence angle normalized sigma-0" (effectively the sigma-0 value at 40 deg incidence angle). The units of A are dB. Typically, 0 < A < -45 dB. However, A is clipped to a minimum -32 dB. Values of A < -32 are used to indicate no data. The B coefficient describes the incidence angle dependence of sigma-0 an has the units of dB/deg. At Ku-band 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 or smaller is used to denote no data. (c) 1999 BYU MERS ============================================================================== Dr. David G. Long long@ee.byu.edu Associate Professor voice: (801) 378-4383 Electrical and Computer Engineering Department fax: (801) 378-6586 459 Clyde Building Brigham Young University Provo, Utah 84602 BYU Electrical and Computer Engineering home page: http://www.ee.byu.edu/ BYU Microwave Earth Remote Sensing (MERS) Laboratory home page: http://www.ee.byu.edu/ee/mers/ or http://mers.byu.edu/ ==============================================================================