The objective of this work is to assemble and cartographically control Thermal Emission Imaging System (THEMIS; Christensen et al. 2004) daytime infrared (IR) and nighttime IR images. In a cartographically controlled mosaic, individual images are registered to one another so that all feature boundaries align. This intermediate mosaic (a “semi-controlled” mosaic) is then registered to a known coordinate system (i.e., tied to ground) and is fully controlled. All needed adjustments are carefully documented and that information is used to correct the position of the spacecraft and update the geometry information in the image headers, and the formal uncertainties of the position of each image are determined. This information is then used to generate updated imaging pointing kernels. Controlled THEMIS mosaics will benefit geologic mapping efforts (superior basemap), landed science operations (site characterization and traverse planning), and orbital observation planning (precision targeting). The control networks that result constitute a (potentially global) framework for the precision cartographic control of existing and future higher spatial resolution data products such as Context Camera (CTX) images, and will allow the registration of historical data sets (e.g. Viking MDIM; Archinal et al., 2003; 2004) to be improved. In addition, the improved imaging pointing kernels will be very valuable to scientists and allow them to perform quantitative analyses with THEMIS images using improved pointing knowledge as well as the precision and accuracy of that knowledge.
Individual documents included in the release of each region include:
Generic file format: THEMIS_Day|NightIR_ControlledMosaic_SiteName_XXSXXE_100mpp.cub
THEMIS infrared controlled mosaic available in ISIS cube, PNG, and GeoTiff formats.
Generic file format: THEMIS_Day|NightIR_ControlledMosaic_SiteName_XXSXXE_100mpp.cub.xml
Includes a description of how the control network and resulting mosaic was generated and any processing issues encountered.
Preliminary updated image pointing kernels
Generic file format: THEMIS_Day|NightIR_SiteName_ck.bc
An image pointing kernel is a file that contains information used to determine observation geometry parameters for an image. This information is needed to convert from a raw image, such as an EDR or RDR, to a map-projected product. The current standard THEMIS image pointing kernel is based on the THEMIS ISIS3 camera model and is the default kernel used by the ISIS program “spiceinit.” The updated image pointing kernels are preliminary, but are nevertheless a significant improvement over the THEMIS camera model kernels. Although THEMIS band 9 (centered at a wavelength of 12.57 µm) was used to generate the control network, the improved pointing knowledge can be applied to all bands (using the ISIS program “spiceinit”) to achieve improved geometry information for any band. To use the improved kernel, point to the kernel file when initializing geometry information using the ISIS program “spiceinit”. An example spiceinit command is:
spiceinit from=I012345678.lev1.cub ck= THEMIS_Day/NightIR_SiteName_ck.bc
When the new kernel is applied correctly to an image, the user will see the following in the image label:
InstrumentPositionQuality = Reconstructed InstrumentPointingQuality = Unknown
If the image time is not contained in the kernel, the user will see the following type of error:
Unable to initialize camera model
CAUTION: The kernels were derived from a control network generated independently for each region. Therefore, the kernel only contains images from within that region. Due to the length of THEMIS images and the orbit path of the 2001 Mars Odyssey spacecraft, there are many images that fall into more than one region. Therefore, A SINGLE IMAGE MAY BE INCLUDED IN MORE THAN ONE KERNEL AND HAVE DIFFERENT GEOMETRY INFORMATION IN EACH KERNEL. Both geometries are correct and accurate, so long as they are used within the latitude and longitude boundaries of the regions for which the kernel was derived. We suggest that you do not mix data from multiple regions/kernel files in a single product, as feature boundaries may not match.
Our future plans include controlling all THEMIS images within ±65° latitude and performing a global bundle adjustment for all images. There will then be a single updated image pointing kernel that includes all THEMIS images within ±65° latitude. This kernel will be a smithed kernel, will be released to the NASA Navigation and Ancillary Information Facility (NAIF), and will be included in future ISIS releases. However, we are releasing these preliminary kernels so that scientists and engineers have access to improved THEMIS image pointing of specific regions on Mars before the final product is complete.
Kernel summary file
Generic file format: THEMIS_Day|NightIR_SiteName_kernel_summary.txt
This file includes the pedigree for the updated image pointing kernel, usage instructions, a listing of all images in the kernel, and all original kernel files used in the control network.
File list for images included in the kernel
Generic file format: THEMIS_Day|NightIR_SiteName_kernel_filelist.txt
- File list for images included in the mosaic
Generic file format: THEMIS_Day|NightIR_SiteName_mosaic_filelist.txt
Some images in the kernel were excluded from the mosaic due to post-calibration image processing problems.