(Special thanks to WSH Crew member Bill Wink for researching the data on these instruments!)
The images for Mars Mappers were obtained from several instruments on the Mars Reconnaissance Orbiter – the HiRISE Camera and the MRO Context Camera (CTX). Here are the technical specifications for each of those instruments:
The Cassegrain objective
with relay optic and two fold mirrors is optimized for diffraction-limited
performance over the long, narrow fieldof-view
(FOV) required for “push-broom” scanning and
imaging. Credit: NASA
- Three mirror astigmatic Cassegrain telescope
- The light reflects off four mirrors and through three filters; a blue-green, red and near-infrared
- Focal length 12000 mm and F/24
- Aperture of telescope 500 mm
- Resolution 30cm/pixel, surface area objects 4-8 ft across can be resolved.
- Resolution 1 micro radian, or 21 arc-seconds/pixel
- 14 detector chip assemblies housing CCDs (charge- coupled devices) staggered with 48 pixel overlap allowing combined images of up to 20000 x 65000 pixels.
- Signal-to-noise ratio of 100:1
- FOV 1.18 degrees x 0.18 degrees
- Data storage 28 gigabits
- Image size 20,000 x 40,000 pixels for B-G images
- Image compressed from 16.4 Gb to 5 Gb before transmission. Compressed in a new format called JPEG 2000
- Each CCD has 2048 12 x 12 micrometer pixels
- Field of View is 1.14° x 0.18°
The HiRISE camera has provided the highest-resolution images yet from Martian orbit. Credit: NASA
The team lead and supplier of CTX is Mike Malin from Malin Space Science Systems
The Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) is currently orbiting Mars and acquring grayscale (black & white) images at 6 meters per pixel scale over a swath 30 kilometers wide. Credit: Malin Space Science Systems
- 350 mm focal length cadiotropic Cassegrain (Maksutov type) telescope
- 6° Field of View
- f/ratio of 3.03 to 3.13
- Resolution is 6 meters/pixel
- CCD image is 5064 x 5064 pixels
- CCD detects broadband of visible light from 500 to 800 nanometers in wavelength
- Typical CTX image can be as wide as 30 km and as long as 160 km
- Pixel size is 7µm
- Study details of the interaction of the atmosphere with the surface of Mars at a variety of scales in both space (local and regional, meter and decameter) and time (days to months).
- Examine surface features characteristic of the evolution of Martian climate over time.
- Monitor locations that show changes resulting from climate or geological processes
- Search for and document new phenomena accessible to the greater spatial coverage (relative to Mars Global Surveyor MOC) afforded by MRO
The CTX wide field of view (6°) compared to HiRISE FOV (1.18°) allows scientists to detect areas of interest and then direct other imaging equipment on the MRO. Thus it finds context for the HiRISE and CRISM – much like using the finder scope on an amateur telescope.
Images are mosaics created by CTX image strips. One of the challenges is getting the images to be at the same time of the day so the shadows are similar. Tanya Harrison, who was once on the Malin Space Science Systems targeting team (at that time they were choosing landing sites for Curiosity) described this process on her webpage .