README File For The PEM WEST-B GMS-4 (GIF Format) Image Distribution 10/18/95 GMS-4/DC-8 MAPPED IMAGES FROM THE PEM WEST-B MISSION Introduction This directory contains GMS-4 images from the period when the NASA Ames Research Center DC-8 aircraft was deployed in the West Pacific, during the GTE PEM WEST-B mission. The images have overlays of the DC-8 flight track with flight level winds, geopolitical outlines, a lat/lon grid, and a calibration bar. There are both infrared and visual images for each flight within the area of 60S-60N, 80E-160W, which includes flights from 2/8/94 thru 3/13/94. There are images every 2 hours thru the duration of each flight, plus another from an hour or two prior to takeoff. However, coverage of some flights is a little spotty due to gaps in the raw data archive. All flights except the transits from Hawaii and to Alaska have image sets at 2 scales, one larger to show upstream weather and one smaller to show the flight track area better. There are 266 images total, taking up about 75 megabytes. This processed data set was created by the DC-8 DADS support project, part of the Medium Altitude Missions Branch at the NASA Ames Research Center. ------------------------- File Organization Images for each flight are stored in separate directories; the directory names are the flight numbers. Flight numbers are formatted 'YYNNFF' where YY is the fiscal year, NN is the mission, and FF is the flight. Filenames for the images are constructed as follows: 'YYMMDDHHMM' for the date and time (UT) of the image 'vis' or 'ir' depending on the image type 'A' for a larger scale or 'B' for a smaller scale image. So, './940115/9403010800irA.gif' would be an infrared, larger-scale image from March 1, 1994 at 0800 UT, during flight 15 of mission 1 (PEM West-B) of FY94. ------------------------- Technical Details The resolution of the original images is 4km/pixel at the satellite sub- point. All processing was done at this resolution or better, and no filtering was necessary. The overall size of the final GIF images is 1010 by 808 pixels, with the satellite picture taking up the pixel space x:30-904, y:24:723, and the remainder used for annotation. This gives an actual image size of 875 by 700 pixels, with an aspect ratio of 1.25, which is maintained in the spatial extent of the mapped images. IR images use a monotonic 256 element grey scale, except that color contours for temperatures between -20, -40, -60 and -80 are used. Also, colors 0-5 (temperatures above 61C) are used for annotation. For color numbers 6-254, the maximum of the RGB triple is always equal to the color number. Visual images use a 64 element grey scale, with RGB values of 0-251, gamma-adjusted to increase the visibility of dim features. Colors 64-69 are used for annotating the visual images. Images were registered to a cylindrical map projection using 3rd-order polynomial image warping with bilinear pixel interpolation, first by using tie-point data supplied with the raw image data sets, and with final adjustment to the map by hand as necessary. Only data inside the area of 60S-60N, 80E-160W was used because distortion increases the farther out you get from the satellite sub-point (roughly 0N, 140E). The page layout was designed to allow easy contouring or cut and paste operations with any graphics package. All processing was done using IDL on a Sun SPARC-station LX. ------------------------- Acknowledgments Susan Cherniss, Darrell Wooten, and Sylvie Faisant (Sterling Software, NASA Ames) supported the acquisition and archival of the GMS-4 data while the DC-8 was in the field. Marion Legg (Synernet, NASA Ames) and Leonhard Pfister (Code SGG, NASA Ames) furnished calibration data and helped fill some gaps in the raw data set. The images were created using GMS-4 data made available at the NASA Ames ftp site explorer.arc.nasa.gov by Milo Medin (Code IDN, NASA Ames), Torben Nielsen and Scott Gennari (University of Hawaii). Many thanks to all of the above. ------------------------- Contacting The Author Please send any comments or questions to carl@cave.arc.nasa.gov, or Carl Sorenson, DC-8 DADS Support phone: (415) 604-4564 NSI Technologies fax: (415) 604-0085 Mail Stop 248-2 NASA Ames Research Center Moffett Field, CA 94035-1000