Frequently Asked Questions
The THEMIS Browse images are available in a variety of formats (PNG, JPEG, TIFF, GIF, and PDF) and can usually be opened in your favorite image display tool.
The THEMIS image files (IMG, QUB, and CUB) files should be opened with an image processing tool that can handle multi-spectral images; NASA-PDS also provides a free image viewer: NASAView.
At ASU, we use either Davinci or JMars for the bulk of our data processing and analysis. We generate and manipulate the projected products using ISIS3, and we frequently compress large images using GZIP (.gz file extension). We also recommend GDAL for simple projection and/or file format transformations.
JMars is a Java-based, geospatial information system developed by ASU originally to support mission operations of the THEMIS cameras. Due to this relationship, JMars provides many specialized features which allow users to easily review, open, and manipulate the THEMIS images. Over the years it has expanded to include data sets from many other Mars missions, as well as applications for the Earth and Moon. Visit the JMars homepage to learn more about this versatile data analysis tool and download a copy for yourself.
All THEMIS images on the website are in the public domain, and should be credited to NASA/JPL/Arizona State University.
Acknowledgment of the THEMIS website and its resources will help ensure the continuing support necessary for the validation, archiving, and distribution of the Mars work at ASU. See Data Citation hints for more example references.
Use one of the following methods to access the THEMIS data and documentation directories:
- HTML Data Access (lower left on Search THEMIS page)
- Browser access to the THEMIS Virtual Volume directory
- Suitable for Wget data retrieval
- Download All as Zip (lower right on THEMIS Image Details page)
- All published products associated with a single Image_ID are compressed into a single ZIP archive and saved to your local system
- Extract the data using the ZIP compression software available on most Windows, OS X, and Linux operating systems
- Please note that although it is not requried, we recommend that you login (upper right in page header) if you wish to use this feature extensively.
Sorry, THEMIS does not have an active FTP site at this time.
The "Search THEMIS" tool is supported by a database that contains the coordinates for at least six points (usually significantly more) outlining the edges of each available THEMIS image. The image will be included in the results table if any of these outline points falls inside your latitude/longitude box, and your remaining criteria are also met.
Note that the previous THEMIS query tool relied only on three coordinates per image; therefore, this new method may return more positive results for the same latitude/longitude box.
If you choose to Register and Login to the ASU Mars Image Explorer website, you will be able to take advantage of the many new features that we are adding to customize your personal defaults and save your favorite queries. Registration is free and we will not send you unsolicited email.
- Standard Data products:
- VIS & IR EDR.QUB
- VIS & IR RDR.QUB
- VIS ABR.IMG
- IR BTR.IMG
- BROWSE (png) & Thumbnail (jpg)
- Special Geometry products:
- VIS & IR GEO.CUB with easy-view png versions
- IR PBT.IMG
- VIS ALB.IMG
- IR DCS.PNG
- VIS RGB.PNG
- Special Derived products:
- IR TIN.CUB
Yes! The THEMIS standard processing is described in the documents here, but you are, of course, always welcome to ingest the published products into your favorite image processing tools. However, we also have created an online processing tool which allows you to complete your own specialized processing using the THEMIS toolset and the ASU-MARS computers. Many exciting and new features for this tool are being developed based on feedback from users like you.
The THEMIS Standard Data products (EDR, RDR, ABR, & BTR) are not projected into any coordinate system. The pixels in these products maintain the time, row, and column ordering (per band) of the raw observation; this arrangement is commonly referred to as "camera coordinates". Be aware that the bands of the QUBE products are not spatially registered within a single image.
The THEMIS Special Projected Products (GEO, ALB, PBT, RGB, and DCS) are map projected, with the coordinate system details documented in the headers and/or available labels. See the available documentation for all projection parameters, but the following guidelines will get you started:
- EQR = EQUIRECTANGULAR, where -60 < center-latitude < +60 (this is a variation of the Simple Cylindrical projection)
- POL = POLAR STEREOGRAPHIC, where max-latitude > +60 OR min-latitude < -60
- SNU = SINUSOIDAL, where -60 < center-latitude < +60
- IR-PBT, VIS-ALB & IR-DCS, VIS-RGB maintain the projection of the source GEO product
Note: there are significant improvements to the THEMIS camera models in ISIS-3; if you have the choice, use ISIS-3 projected products over ISIS-2 projected products.
The five color filters of the THEMIS VIS camera do not span the full range of colors available to the human eye, so extensive processing, and an artistic touch, is applied to convert a raw image into an approximately "true color" image. Several of the THEMIS Team members are experts in VIS spectroscopy and have used their experience with the Hubble Space Telescope (HST) observations of Mars to generate a limited number of VIS color images. Their multi-step process, described here, is now used to generate Special VIS-RGB projected products.
Note: that the long edges of THEMIS VIS images commonly contain color artifacts that do not represent true surface variations and may cause the overall color variation of the scene to become slightly exaggerated.
The four panels of the IR-DCS browse product are (from left to right):
- DCS where RGB = bands 875
- DCS where RGB = bands 964
- DCS where RGB = bands 642
- Stretched Brightness Temperature
Long, narrow images represent a single observation with the THEMIS camera.
Large, boxy "images" represent a mosaic of multiple, overlapping images collected throughout the mission and saved as a single file. Various image processing techniques may be applied to hide the edges of the individual images.
The Mars Odyssey spacecraft follows a polar orbit, but never flies perfectly along the meridian lines nor directly over the poles (+/- 90 latitude). The fact that THEMIS images are usually longer along-track, as compared to their cross-track width, combined with the slightly offset polar orbit, results in images that appear to "lean" when displayed in map projections with north up. Images that appear to lean to the right (like "/") were collected on the descending orbit node; images that appear to lean to the left (like "\") were collected on the ascending orbit node.
Odyssey Extended Mission orbit changes had the effect of changing the local time of each node:
- descending orbit node images collected before orbit 55600 usually have day timestamps (6am-6pm)
- descending orbit node images collected after orbit 55600 usually have night timestamps (<6am or >6pm)
The standard parameters used when generating THEMIS Polar Stereographic products approximately align the along-track axis of the image vertically in the resulting projection; when displayed, the start of the image as collected is at the TOP. For images completely collected during the descending orbit node, this is equivalent to the common "north-up" convention; for images completely collected during the ascending orbit node, this is equivalent to "north-down". For images that cross the highest polar regions (i.e. starting during one orbit node and ending during the other node), the north pole will be off to the right or left in the map projection; use the North Azimuth Angle parameter associated with the image to exactly locate the pole.
While the Context image is oriented as close to the common "north-up" convention as possible, the available Browse Format images do not necessarily follow this convention. In these cases, the FLIP button allows users to match the Browse image orientation to the Context image orientation.
Browse Formats that are presented "as-collected" during the ascending orbit node may benefit from a FLIP; these include IR-Browse and BPOL browse (see FAQ about North in Polar images). Similarly, RGB and DCS browse that are generated from polar projected images may need a FLIP to match the Context image.
An additional use of the FLIP button is to reverse the effects of the sunlight direction optical illusion in some images. Most likely, your eyes have become accustomed to seeing topographic features in THEMIS-VIS with sunlight coming into the image from the left side. Later in the mission, the Odyssey orbit changed such that the sunlight is coming into the image from the right side. This can create the optical illusion that craters and channels (topgraphic lows) are domes and ridges (topographic highs), and vice versa; use the FLIP button to reverse the effect and correctly "see" the features.
THEMIS is a thermal emission imaging system. It contains two independent multi-spectral imaging sub-systems:
IR = a 10-band thermal infrared imager
VIS = a 5-band visible imager
A full description of the THEMIS instrument and a tutorial on spectroscopy is available here.
- The IR bands (1-10) used by THEMIS are centered at the following wavelengths (in microns):
- 6.78, 6.78, 7.93, 8.56, 9.35, 10.21, 11.04, 11.79, 12.57, 14.88
- (Yes, the first two filters have the same spectral center.)
- The VIS bands (1-5) used by THEMIS are centered at the following wavelengths (in microns):
- 0.425, 0.540, 0.654, 0.749, 0.860
The nominal resolution of the IR camera is about 100m/pixel.
The nominal resolution of the VIS camera is about 18m/pixel.
The resolution of either camera can be modified by spatial summing applied onboard before the images are downlinked; the image header and the Image Data table on the Details tab include the actual pixel resolution for each image.
- The schedule of previously released data is available here. In general, new data is released six months after ground receipt of the last raw data within each three month collection period:
- Data Collection == Released
- Jan–Mar (Year1) == Oct Year1
- Apr–Jun (Year1) == Jan Year2
- Jul–Sept (Year1) == April Year2
- Oct–Dec (Year1) == July Year2
JPL provideds a subscription service that will notify you weekly of the new THEMIS daily images and quarterly of new data releases. You can sign up for the service through PDS Subscription Service.
You may also select to receive Press Releases for a variety of other NASA space topics from the JPL Newsroom.
The THEMIS investigation has several science objectives:
- to determine the mineralogy and petrology of localized deposits associated with hydrothermal or sub-aqueous environments, and to identify sample return sites likely to represent these environments.
- to provide a direct link to the global hyperspectral mineral mapping completed by the MGS-TES by utilizing the same infrared spectral region at high (100m) spatial resolution.
- to study small-scale geologic processes and landing site characteristics using morphologic and thermophysical properties.
- to search for pre-dawn thermal anomalies associated with active sub-surface hydrothermal systems.
- to investigate the processes operating in the north and south polar caps at all seasons.
- to determine the spatial and temporal distribution of atmospheric dust and water-ice areosols.
Yes. Both water and ice are easily detected in the wavelength bands of the IR camera.
THEMIS can see through a small amount of atmospheric dust; however, even a small layer of surface dust (~100 um) will obscure any underlying thermal IR signatures. Diurnal thermal conductivity can occur through several centimeters of dust, but will only change the temperature of the dust on top.
See global dust maps generated from recent THEMIS data here.