This web based interface is designed to provide a quick and relatively simple way to process THEMIS infrared data. THEMIS data is rich in information, but requires a number of unfriendly and complex processing steps to be performed on the data in order to use it properly. The interface provides the ability to produce advanced THEMIS data products without the necessity of specialized equipment, software, and arcane knowledge of the details of THEMIS data and its processing software. We hope this will ensure the broadest possible use of the THEMIS dataset to maximize the science return from this investigation.
The Main (batch list) page gives a list of all batches that have been submitted by the current user. Each batch contains 1 or more output files from 1 or more image ID's base on the options selected on the Batch Submission Page. To submit a new batch, click on the New Batch link near the upper right of the page. Any batch may be viewed in more detail by clicking on any text associated with the batch (ID, Created, Status...).
The Batch Description Page can be accessed by clicking on any batch in the Main (Batch List) Page. Batch ID, user entered description, and the processing options selected from the Batch Submission Page are shown at the top. At the bottom of the page is the list of output files requested for the particular batch and clicking on any of the text will link or download the file if the status is complete. Product is the THEMIS image ID used to make the file, type is the file format (ISIS CUBE, PNG, JPG, or TIFF), status is the current status of the file (submitted, script running, waiting, generating, complete, failed), and options give the processing options unique to the file within the batch.
This page allows the user to construct a customizable THEMIS IR image data request. There are a number of processing options as well as output format options, which are described below. After the desired options are filled in, the submit query button will lead to a confirmation page which summarizes the processing and output request. Upon confirmation, the browser will return to the Main (batch list) page.
Image IDs Image IDs are the images that are listed for processing. These follow the Ixxxxxyyy convention where I stands for infrared image, xxxxx is the orbit number, and yyy is the image number. An example is I01920047, which is an infrared image and was the 47th image taken during orbit 1920. The search option leads to the THEMIS PDS site and allows for a search for image ID's based on a number of criteria (e.g. lat, lon, temperature, time of day/season...).
Job Description The job description is user input text that helps identify for the user the set of images submitted.
Undrift / Dewobble (UDDW) The Undrift-Dewobble filter is applied to the THEMIS IR-RDR QUBE to remove data value fluctuations caused by changes in the temperature of the IR detector array. Band 10 values remain unchanged.
Rectify Rectify eliminates most of the black space present in a projected THEMIS IR image by shearing the image to produce a rectangle aligned in both the x and y directions. This step produces a much smaller uncompressed image and is necessary for the deplaid processing to occur.
Deplaid The deplaid filter is applied to remove row and line correlated radiance spikes from the ISIS projected THEMIS IR radiance data. Deplaid uses spectral information to remove line and row correlated noise that is not correlated between spectral bands. The effectiveness of the deplaid filter is associated with the number of surface radiance bands available from the image. Deplaid must be used with rectify.
Radiance correction (Radcorr) / Automatic radiance correction (Auto-radcorr) Radcorr and autoradcorr remove atmospheric emitted radiance from the THEMIS radiance images. Radcorr requires a user defined box within the image (box selection features not yet implemented). Autoradcorr automatically generates and removes atmospheric emitted radiance with no user input required. The radcorr algorithm is described in Bandfield et al., JGR, 2001JE002289, 2004. This algorithm should only be used on projected 10 band THEMIS IR radiance images and will have no effect on other band combinations.
Unrectify Unrectify returns a rectified THEMIS IR image back to its original projected state. This adds considerably to the file size.
For the best results and least distortion of an image, sinusoidal equal area projection is recommended for images between +/- 60 latitude. Each image will have a slightly different projection, which prevents perfect alignment for mosaics. The simple cylindrical projection will be uniform for every image, which allows for mosaics. However, at higher latitudes (>+/-30), features become increasingly distorted. The polar projection is necessary for viewing high latitude images without massive distortion.
Type
SINU – Sinusoidal Equal Area (default)
SIMP– Simple Cylindrical
POLA – Polar Stereographic
NONE – no projection (not yet implemented)
Meridian Longitude of the central meridian of the image (-- is default)
Latsys Projection latitude type OCENTRIC (default) or OGRAPHIC. Planetocentric latitude is defined as the angle between equatorial plane and a line from the center of the body to a given point. Planetographic latitude is defined as the angle between the equatorial plane and the normal to a spheroidal reference surface on the given point. Planetocentric is more commonly used with newer datasets.
Lonsys Longitude type is 0 to 360 (default) or -180 to 180.
Resolution Resolution in kilometers/pixel of the projected data. The natural resolution (~95-105 m/pixel) is default. -- will produce the natural resolution appropriate for spacecraft altitude, etc...
The crop function returns a geometrically projected THEMIS IR image only with in the specified latitude and longitude bounds. With the default settings (--), the entire image is projected and latitude and longitude bounds are automatically selected that are sufficient to include all of the image data. Pad ensures that the full longitude bounds of the images is included in the final image. The east longitude (see lonsys) system is used.
Brightness Temperature The brightness temperature function converts all available THEMIS IR-RDR radiance bands to the blackbody temperature for the equivalent radiance integrated over each THEMIS bandpass. Brightness temperature can be used on either projected or unprojected data.
Surface Temperature The surface temperature function produces an image of the highest brightness temperature in bands 3-9 for each pixel. This approximates the surface temperature even though the atmosphere is not entirely transparent and surface emissivity is not exactly unity. Surface temperature is not recommended for colder surface (<220 K). In these cases the brightness temperature of THEMIS band 9 is likely to be more accurate.
Emissivity Emissivity is the ratio of the measured radiance in each THEMIS band to the Planck radiance of the highest brightness temperature (surface temperature) in THEMIS bands 3-9. Radiances are integrated over each THEMIS bandpass.
Output Data Formats
ISIS Cube The ISIS cube output produces an image cube file with full attached header and suffix information. ISIS cubes can be read into ISIS (http://isis.astrogeology.usgs.gov), davinci (http://davinci.asu.edu), and other specialized image processing programs. All isis files are compressed in gzip format.
Band The band of interest function selects only the specified bands from a THEMIS image.
Backplanes The Backplanes function produces ancillary image plane data associated with each THEMIS IR pixel. This includes associated geometry, such as latitude, longitude, and local solar time. Backplanes appear as suffix data in the isis cube.
8-Bit Grayscale The 8-bit grayscale function converts the output data to single 8-bit images with values between 0 and 255. Individual bands may be selected, common image formats are chosen, and stretch options are provided to scale the data appropriately.
Format The format option allows the specified image format to be output. This includes compressed PNG, and JPG files, uncompressed TIFF, and uncompressed ISIS format. The ISIS format files can be used as input files for display in JMARS. A separate image is produced for each band selected. ISIS files are compressed in gzip format.
Standard Deviation Stretch / Running Stretch/Linear Stretch The stretch, running stretch, and linear stretch functions scale the input THEMIS data to 0-255, producing a byte image suitable for 8-bit grayscale output. The average output DN is 127 with a specified standard deviation (default is 40). Running stretch performs the stretch function on user specified (default is 1000) line segments of the THEMIS IR image to enhance local surface features. Linear stretch allows the user to specify the input and output value limits to scale the data.
3-Band Decorrelation Stretch (DCS) / Running DCS The DCS function produces a color image that enhances the spectral variations present in the three bands used to produce the image. For more information, see Gillespie et al., Rem. Sens. Environ., 42, 137-145, 1986. The running DCS function performs the DCS function on separate user defined (1000 line is default) segments of the THEMIS IR image and reassembles them. This enhances local spectral variations over regional spectral changes. The DCS function must be used on projected THEMIS IR radiance or emissivity images and returns a three band byte image.
Tilt removal The Tilt removal function performs a running remove tilt on every xy plane of the data (band independent). This function performs an individual removal of tilt on every sub-section of the array defined by an x and y dimension. It then uses an overlap of half of the defined size to blend it with the next section of the data. This is done so there is no visible seam and the tilt removal is esentially "running" or changing over the whole data set. This process helps eliminate tilt which is variable over the length of the image (especially in long images).
Streak removal Streak Removal (destreak) function removes the noise known as "streak" from THEMIS spectral images. Streak only occurs in approximately 1% of the data and may only be visible in bands 1 and 2 of emissivity images.
White noise Removal 1 and 2
Noise removal algorithms for THEMIS radiance cubes.
white noise removal 1 - It converts the data to emissivity, smoothes and recombines with unsmoothed brightness temperature.
white noise removal 2 (PCA) - Advanced White noise removal algorithm for THEMIS radiance cubes.
Each band of radiance is converted into a percentage of the luminosity, the integral of the radiance over all bands.
This 'relative color space' is then convolved and then multiplied by the luminosity to regain radiance units.
GZip Compression All requested products are compressed using GZIP software (suffix .gz) for storage and transmission. GZIP software is commonly available on UNIX systems or is available as a free download. For non-unix based systems, we recommend the 7-ZIP software, also available as a free download.
JMARS Compatible