|
The Imager for Mars Pathfinder (IMP) and the Surface Stereo Imager (SSI) are nearly identical. The IMP flew on the Mars Pathfinder mission, and took more than 16,000 images of the Martian surface in Ares Vallis between July 4 and September 27, 1997. The SSI will be launched in January 1999 as part of the Mars Volatiles and Climate Surveyor package, on the Mars Polar Lander '98 mission. In late 1999 it will land near the south pole of Mars. In this page, for convenience, IMP images are discussed. However, the same facts apply to SSI images.
|
 |
As you may have learned in "How the IMP works," the filter wheel is one of the most important parts of the IMP. It enables us to take many different types of images, including color and stereo (3D) images. The filter wheel works by preventing all but a small range of wavelengths from entering the camera. For example, the 440 nm blue filter only lets blue light, at the 440 nanometer wavelength, pass through the filter and enter the camera.
In
this image, the filter wheel is shown in blue.
|
In this image, we see the path of light entering the camera. The entire filter wheel is not pictured in this diagram, but the black lines indicate where filters (the gray circles) would block out all light except certain wavelengths. |
but blue light passes through
the 440 nm filter.
Twelve of the filters in the IMP are used to examine the geology
of Mars. These filters rely on the fact that different minerals
reflect varying colors (wavelengths) of light. Some of these subtle
differences may not even be visible to the human eye, but individual
filters can be "tuned" to specific spectra (colors of
light), in order to make them very visible in the images. Geologists
have made predictions about what minerals can be found in the
area, and the filters geology filters have been picked accordingly.
Eight filters are included in the camera to enabled scientists
to look at the atmosphere. Mars's atmosphere is primarily carbon
dioxide, much thinner than our own atmosphere, and extremely dusty.
The atmophere filters were used to take images of the sun.
These images are useful in determining how light interacts with
the Martian atmosphere. With these images we can investigate
many qualities of the atmosphere, including opacity, amount
of dust, size of dust particles and amount of water vapor.
There is another filter which has to do with dust, the diopter
filter. The Danish collaborators from the Niels Bohr Institute
made some specially designed magnets, whose purpose is to collect
magnetic dust as it settles out of the atmosphere. Most
of the magnets, placed strategically on the lander, were imaged
with the normal geology filters, however, they also had their
own special filter: the diopter filter enabled the IMP to have
a high resolution view of the dust which collected on the tip
plate magnet, very close to the camera's eyes. These experiments
are interesting because dust plays such an important role in the
Martian environment
.
The IMP's two "eyes" are what enable scientists to create stereo (3D) images -- that is, images which demonstrate the depth of a scene. These images have more than entertainment value, they make it possible to gauge distance with a technique similar to "range finding." Differences between the scene viewed by the right eye and the scene viewed by the left eye can indicate the distance to objects in the scene, as well as their distance from each other. The filters used for stereo were geology filters. Most stereo images were taken with the 670 nm (red) filters. Of the geology filters, only two were able to be used for both eyes, the red and the blue (440 nm).