SHARP is a freely available IDL-based viewer for MODIS Airborne Simulator (MAS) image data. The program offers a point-and-click interface with the following features:

• Selection of any scene (716x716 pixels) in a MAS HDF (50 or 12 channel) or MASTER HDF file,
• View any of the available spectral bands (with automatically generated title and color scale),
• Automatic scaling to reflectance or brightness temperature units,
• User selectable image units (reflectance/temperature or radiance),
• Continuous display of data values (Pixel, Line, Sample, Scanline, Time, Lat, Lon, Value) under cursor,
• Image creation via user defined linear band combinations (e.g. NDVI),
• Enhance/stretch image with B&W or color lookup tables,
• User selectable scaling of image data (including 2% histogram clipping stretch),
• Interactive scatter plots with,
1. User selected image regions (rectangle, circle, polygon),
2. User selected X and Y axis band formulas,
3. User selected X and Y axis limits,
4. Select up to 10 regions (10 different colors),
5. Save region data (along with time/lat/lon) to an ASCII file,
• 3 band RGB image display (2% histogram clipping stretch or histogram equalization, grey flip optional),
• Overlay of cloud mask results and individual cloud mask tests (with 'Test not run'),
• Projection onto a map base,
• Overlay of HIS field of view locations and times (requires HIS data),
• Dynamic image zoom and roam window,
• GIF or Postscript output (WYSIWYG) of whatever is displayed onscreen.

Version 1.39 (6/15/99)

• The IDL command line is now available when SHARP is running (you can run multiple instances of SHARP),
• Many reliability improvements, including the addition of functional window menus to all dialogs,
• Added the IDL command line procedure MAS_FLAT_FILE for extraction of binary image data,
• Added information on how to make SHARP installation more streamlined.

• Title now includes field experiment name, time at center pixel, and flight track number,
• Legend now includes orientation data for center pixel (lat, lon, heading, solar zenith and azimuth, relative azimuth),
• Input and output dialog boxes are more intelligent,
• Pixel data values are now displayed in RGB mode,
• Now you can save all 50 bands within selected plot regions,
• Added a program information dialog box available at startup,
• Added a test at startup to ensure that sufficient colors are available in the current IDL session,
• IDL 5.0, 5.1, and 5.2 versions are now available.

• Reflectances in bands 1-25 are now computed correctly (thanks to Steve Platnick at GSFC),
• Map projection now always in correct orientation,
• TVRD is no longer used (fixes some problems seen in Zoom window on TrueColor displays),
• Data value display line is now active only after a file has been loaded,
• Scene select image now uses 2% histogram clipping stretch for better contrast,
• Added lat/lon grid checks in map projection to handle MASTER data.

The program will run on any platform where IDL 5.0, 5.1, 5.2, or 5.3 is installed. Just follow these steps:

(1) Check that IDL is installed. If you don't have it, download the IDL 5.2 demo version from the RSI FTP site. All SHARP functions except GIF and Postscript output are available in IDL 5.2 demo mode.

(2) Download the required program files for your version of IDL (Windows/UNIX users click right mouse button then 'Save Link', Macintosh users click and hold mouse button then 'Save Link'):
    (a) Save file for IDL 5.0.2 | IDL 5.1 | IDL 5.2 | IDL 5.3 | IDL 5.4 () (save the file as 'sharp.sav')
    (b) Startup file

(3) Download sample MAS data files (use 'gzip -vd' to decompress):
    MAS imagery sample (40MB) AND MAS cloud mask sample
    (if you don't have gzip, download gzip for DOS or gzip for Unix)

(4) Change directories to the location of the downloaded files and then do the following:
    Start a new IDL session, and type
        @sharp_startup

To streamline the installation of SHARP under UNIX:
1. Make a new directory under your IDL installation directory named 'user_contrib',
2. Copy the SHARP save file 'sharp.sav' to the user_contrib directory,
3. Copy the SHARP startup file to 'idl_startup.pro' in the user_contrib directory,
4. Remove all lines in 'idl_startup.pro' after 'xmanager, catch = 0',
5. Add the full path of the user_contrib directory to the IDL_PATH environment variable (or use IDLDE preferences),
6. Set the IDL_STARTUP environment variable to the full path of the file 'idl_startup.pro' (or use IDL preferences).
All users who wish to use SHARP should repeat steps 5 and 6.

Command line tools

Several SHARP users have asked if there is an easy way to extract binary image data from MAS HDF files. For this reason I have made available the IDL command line procedure MAS_FLAT_FILE, which can be used to extract a single band of MAS image data to a flat binary (32 bit float) file. For an example, download the procedures below, and then in IDL type

IDL> doc_library, 'mas_flat_file'

The procedures required are
MAS_FLAT_FILE: extract a single band of image data, and optionally the associated geolocation data
MAS_READ: read data from a MAS HDF file (used internally by SHARP),
MAS_FILE_TYPE: identify the type of a MAS data file (used internally by SHARP)
BRIGHT_M: Compute equivalent brightness temperature given Planck radiance (used internally by SHARP).

Notes on running the program

Additional data:
MAS and MASTER data in HDF format are available free of charge. See the MAS Web site or MASTER web site for details.

Windows/Macintosh support:
The program has been tested in IDL 5.1 under Windows 95 and NT 4.0. It should also run on a Macintosh, but I have not tested it.

User Updates:
In order to help me keep users on Unix platforms informed about SHARP updates, I have added a SPAWN command to the SHARP startup file which automatically sends me an email message containing your OS version. If you don't like this idea, please feel free to comment out or remove these lines. Please note that this happens on Unix platforms only.

Limitations of the current version

IDL 5.2 problems in Win95/98 (note that this problem is fixed in IDL 5.3):
Testing has revealed a problem when running in IDL 5.2 for Win95/98. Users *may* see a program crash when trying to open a new HDF file in SHARP, or MAS_FLAT_FILE. RSI Technical Support has been notified of this bug, and they were able to reproduce the error under Win95, but not Win98. My own Win95 and Win98 systems are both affected by this bug. According to RSI, they do not plan to fix the problem at this time, because they claim it is unclear whether this is an IDL problem, or a HDF problem. The only action I can recommend is to use IDL 5.1 instead. Please let me know if this bug causes you serious problems, and I'll try and work something out.

IDL True Color mode:
SHARP will run just fine in IDL True Color mode (e.g. when you have a 24 bit display on a PC). The only oddity is that when modifying the color table with the 'Colors' tool, color table updates are not immediately displayed in the image. You must re-select the current band to update the image colors (this is a limitation of IDL).

Fonts:
The program tries to pick suitable onscreen fonts. However on some Unix boxes (especially X terminals), the font selection is not optimum, and titles/legends do not fit properly.

Scene selection in RGB mode:
A color table anomaly is seen when using scene selection in RGB mode. To get around this, switch back to single band or math mode before invoking scene selection.

MAS HDF data files with less than 716 scans:
Currently the program will not read MAS HDF data files with less than 716 scanlines.

Credits

Paul van Delst collaborated with me on the first SHARP prototype (not released to the public) and without this experience, I could not have created the version available here.

Kathy Strabala, Richard Frey, and Steve Ackerman at CIMSS UW-Madison were instrumental in defining the features and design of SHARP. Bryan Baum (NASA Langley), Steve Platnick (NASA GSFC), and Zhengming Wan (UCSB) all provided very useful feedback and suggestions.

David Fanning provided an excellent reading list and a wealth of examples from which I derived a great deal of inspiration.

MAS data are processed by Paul Hubanks at NASA GSFC, and Greg Cleven at NASA Ames.

This work was funded by NASA under grant NAS5-31367 as part of Paul Menzel's investigation for the MODIS Science Team.

Feedback

Please let me know if you have any problems, comments, or suggestions regarding SHARP (I like to hear from users!). It is a work in progress, and features are still being added. The design of SHARP was largely driven by the needs of in-house users, and I am eager to hear suggestions from outside users. I am developing a SHARP-like program for viewing MODIS scenes, which I plan to release to support Terra operations in the spring of 2000.