To give you some idea as to the size of a HiRISE image, I’ve put together a few screenshots from our planning software, HiPlan. These images compare the HiRISE footprint with that of the the THEMIS instrument aboard Mars Odyssey. These screenshots are shown below as thumbnails; click on a thumbnail to see the screenshot at its actual resolution.

I should note that these are not planned to be actual HiRISE images; I was using HiPlan in test mode while working on the display of the individual HiRISE CCD footprints.

Take a look at this screenshot. It covers a small region of Mars roughly one degree across and slightly less than a degree tall:

The low-resolution background is THEMIS daytime infrared imagery at 256 pixels per degree; it is an amalgamation of several such infrared THEMIS images. This view was displayed in HiPlan at 1024 pixels per degree, so the background looks quite blocky.

The sharper region down the center of the screenshot is the upper portion of a single THEMIS visible spectrum image. It is a much higher-resolution image, so it appears quite a bit sharper than the background. The black border surrounding the visible spectrum image is an artifact of the simplified image processing used in HiPlan; in order to show quickly multiple sets of data overlain atop one another, corners almost literally have to be cut.

The colorful, translucent rectangle cutting across the crater is a typical HiRISE “footprint”—that is, it is the area of Mars that would be imaged by our camera were we actually to take this picture.

You might know that HiRISE consists of 14 individual CCDs, arranged in a row 10 CCDs across with the remaining four positioned in the middle of the array. This arrangement is illustrated in the screenshot by the reddish and greenish rectangles within the blue rectangle.

An additional level of zoom in the planning software shows these red and green rectangles more clearly. This second screenshot covers an area about a half-degree wide and a half-degree high; the image data are shown at 2048 pixels per degree:

Each of the red rectangles represents one of the ten red-filter HiRISE CCDs. You probably notice that there are only eight visible. The other two are hidden by the green rectangles.

Each of the green rectangles represents one of the blue-green filter HiRISE CCDs. As mentioned, they’re covering up the central red-filter CCD rectangles. They’re also covering up the two near-infrared filter (NIR) CCD rectangles, which would be drawn a translucent white. If I had set these HiRISE images up without the blue-green CCDs active, you’d see the NIR CCDs clearly.

The next two screenshots form another pair from roughly the same region of Mars. The first is with HiPlan zoomed to 1024 pixels per degree, covering about one degree of width of the surface of Mars:

The blue lines running through this screenshot canted slightly to the HiRISE footprint are THEMIS footprints. I’ve chosen not to have HiPlan fill them in.

The second is the same area zoomed to 2048 pixels per degree; it covers a region about a half-degree across:

What about the blue regions at the ends of the HiRISE footprints? In order to coordinate HiRISE observations with those planned by other instruments aboard MRO, we always plan on slightly larger observations than we really take. In addition to making the coordination planning easier, it allows us to change the size of our observation or move it around slightly after the spacecraft-level instructions have been sent, but before our actual instrument instructions are delivered.

Normally, we center our actual observation within the blue planning zone. We could easily adjust it, however. In the case of the second set of screenshots, for instance, we might decide to slide our observation downward towards the couple of small craters near the bottom of the planning zone. We can do so without interfering with the operation of the spacecraft as a whole and without having to re-plan our coordination with the other instruments.

I started this post by claiming it might give you a feel for the size of a HiRISE image. I haven’t forgotten. If you click on one of the thumbnails above, you will get a full-size rendition of the planning screenshot. Each screenshot is 1024 pixels wide.

Take a look at just one of the red-filter HiRISE CCDs (or one of the blue-green filter CCDs; I’m not picky). If HiRISE were to take the picture planned here in these screenshots, you could fit two of those screenshots, side-by-side, across that red-filter CCD outline, and you could fit a few dozen down its length.

We’ll be able to display acquired HiRISE images in HiPlan in the near future, much like we can see acquired THEMIS images, though we’ll probably never be able to display them at full resolution. They’re too big!

One final note: HiPlan is built atop an application developed up at ASU called JMARS. Not coincidentally, the THEMIS team uses JMARS to plan their images.