Emily Lakdawalla continues her excellent blog coverage in this article, which does a great job of explaining some of the reasons why this image was especially difficult to take. Along the way, she includes a tutorial on TDI (Time-Delay-Integration), written by one of the engineers that helped build the instrument. TDI is the method HiRISE uses to gather lots of light into its CCDs, and it’s one of the reasons we get such high signal-to-noise in our images. It’s a complicated concept, but it’s an important one for understanding HiRISE’s incredible imaging abilities, as well as its limitations.

From her blog post:

This is a fascinating story showing how necessary it sometimes is to have a deep understanding of an instrument in order to understand the data that comes from it. …It can be dangerous to read too much into space images until you have studied how the cameras really work.

It’s a great post – she deserves a cookie!

View Images

There are, as always, many magnificent images here. Some of the noteworthy observations are:

PSP_001521_2025 and PSP_001501_2280: On the HiRISE web site you can see diagrams made by Tim Parker show the locations of various parts (lander, backshell, heatshield or parachute) for Viking Lander 1 and Viking Lander 2. It’s possible they aren’t in the color strip (I haven’t found them)!

PSP_001508_1245 and PSP_001510_2195: These two exhibit a “glow” pattern of saturated pixels due to high TDI (Time Delay Integration) settings on the blue-green CCDs. (All of the exposure settings are chosen for each observation based on a photometric model of the scene).

PSP_001538_2035: This is a rim-to-rim section across a crater called Tooting that is about 30 kilometers in diameter. It’s also interesting to note how the altitude of the rims, when combined with the large off-nadir roll angle (23 degrees), leads to an oddly bowed geometric projection. But it is correct; as the terrain rose, fell, and rose again from HiRISE’s angled point of view, the center of the ground track deviated slightly east or west from a true great-circle line.

PSP_001558_1325 and PSP_001593_2635: These dune fields are striking, forming incredible patterns.

PSP_001582_2245: Looking like a super-sized area of dried mud, the polygonal cracks in this image are amazing.

Updated (2008-Apr-10)

We had the difficult detective job of figuring out what went wrong. It was clear early on that the instrument overheated, but we couldn’t figure out why. Our tool that predicts the temperatures (”HiTemp”) didn’t predict anything that hot. We didn’t take a really large image, which would heat us up (at least, nothing bigger than normal! ). The local operations team worked with the health & safety people, the spacecraft engineers at LMA, and some of the software developers at Ball Aerospace that originally designed HiRISE. Together we all investigated the problem.

We studied the telemetry (information from the spacecraft), the details of the commands that were sent to the instrument, and we re-modeled the temperatures and memory use. The problem was complicated by several other unusual events that occurred around the same time: First, the memory on board the spacecraft (the “Solid State Recorder”, or SSR) had filled up because one of the dishes of the Deep Space Network was broken. This meant we couldn’t send data back to Earth, so it piled up in the memory until it overflowed. Second, HiRISE’s “keep-alive counter” was withheld. This is a steady heartbeat HiRISE sends to MRO that indicates HiRISE is still running. After a certain number of heartbeats are missed, MRO will safe HiRISE. Also around the same time, there were some errors in the spacecraft’s software. The timing was also mysterious: HiRISE safed about 15 minutes after an image. This is a long time afterwards – the image should have been completely done within just a few minutes. Instead, the temperature sensors showed that we continued to heat up for 15 minutes!

Finally, after a day of research, we found an answer. What happened was this: First HiRISE did all the setup steps to take an image (set the number of lines, etc.). One of these steps turns on the CCDs (sensors) in the camera. Then, right before it was about to actually expose the image, it found out that the memory was full. Since there wasn’t enough room in memory for the data, it didn’t take the image. However, everything was left turned on! So with everything powered on, we continued to heat up until we reached the limits we have set to protect the instrument. This withheld the keep-alive counter, and HiRISE safed. So in fact, the instrument worked exactly as it should have, in order to keep itself out of danger. It was just an unexpected response to this unusual situation.

With the help of the LMA engineers, we were able to power HiRISE back on the following day and start imaging again very quickly. Thankfully, we were up & running in time for another very special observation that I’ll be writing about soon….

The solution for many NASA missions has been the development of the centralized Planetary Data System (PDS). The PDS is several things: a collection of websites, a search capability, an archive, a database, a learning tool, etc. The PDS Imaging Node is located at http://pds-imaging.jpl.nasa.gov/ and acts as “the curator of NASA’s primary digital image collections from past, present and future planetary missions.” These missions include Voyager, Galileo, Cassini, and many more. Now the Mars Reconnaissance Orbiter (MRO) has been added to the list, with the HiRISE team releasing our first several months of image data.

• MRO PDS page: http://pds-imaging.jpl.nasa.gov/Missions/MRO_mission.html
• MRO Product Search page: http://pds-imaging.jpl.nasa.gov/search/index.jsp
• HiRISE Volume: http://hirise-pds.lpl.arizona.edu/PDS/

What we have released is an archive of the HiRISE Experiment Data Records (EDRs) and Reduced Data Records (RDRs). EDRs are in the *.IMG file format and represent individual CCD channels (remember, there are 14 CCDs in the HiRISE camera and two channels per CCD, for a total of 28 channels). These EDRs are cleaned up, calibrated, stitched together, and mapped to Mars’ geometry, resulting in the RDR products. RDRs are in the *.JP2 and *.LBL formats. JPEG2000 is the technology that enables us to offer our gigantic images to the scientific community and the public in a timely and efficient manner. An observation’s image data are in the *.JP2 file and its meta data are in the detached *.LBL files. To view these products, JPEG2000 compatible software is required (see our site for a list of offerings).

While we have been trying to release up to five captioned images a week for the past few months, the PDS release represents several hundred images, most of them without captions. You can find them using the PDS search capabilities, and you can also find them on the new HiRISE site, unveiled today to coincide with this first PDS release. The redesigned site focuses on the images while providing, hopefully, a more user-friendly interface:

• HiRISE Site: http://hirise.lpl.arizona.edu/
• “About Our Redesign”: http://hirise.lpl.arizona.edu/profil.php
• Images released to the PDS: http://hirise.lpl.arizona.edu/pds_release.php

As word gets out about the new site and the PDS release, you may experience some site slowness. Please be patient, and thank you for your interest!

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.

The HiStitch pipeline combines the matching HiCal products for the same CCD into one more-or-less lined up CCD cube file. HiccdStitch combines these HiStitch cubes into RED, IR, and BG mosaics.

Both pipelines take some time, as overlapping pixels are accounted for and brought together. After these mosaics are created, additional steps create smaller jpeg files for easier viewing, and full-sized jpeg2000 files. We use these jpeg2000 files for validating our images.

There are later pipelines, but we first validate the HiccdStitch products: Did the previous pipelines work correctly? Did the uplink team command the camera correctly? Is there haze or clouds obscuring our view of the surface?

If everything looks good, and we have received the correct reconstructed SPICE ephemeris data, then the geometry pipelines are invoked. These pipelines project the images mathematically to a model of Mars and add geometry data to the images so that each pixel becomes a point on Mars with latitude and longitude coordinates.

You should know by now the route our data takes: from the HiRISE camera on MRO to storage to spacecraft radiation to the Deep Space Network radio telescopes here on Earth to the ground data system network to JPL in Pasadena, CA to the University of Arizona campus network to our servers in the HiRISE Operations Center. Our Watchdog software, well, watches the JPL servers for new HiRISE raw image data. When it sees a new raw channel file (2 channels per CCD, up to 14 CCDs per observation), Watchdog flags that file as ready to be downloaded by HiDog.

HiDog is the first automated pipeline. It wakes up every few minutes to see if the Watchdog has flagged any new files (basically, it is checking a sources table in our database). If there is nothing new in the sources table, then it goes back to sleep. If there is something new, HiDog wags its tail, rapidly downloads the file, checks to see if there are any gaps in the data, and then tells the next pipeline that a new image channel has arrived in Tucson, ready for further processing. Then, it checks to see if there are any more files ready for downloading, and goes back to sleep if there are not. Sweet dreams, little doggy.

Over and over again, 24 hours a day, 7 days a week, the Dogs are ready and waiting for the latest HiRISE data from Mars.

Next time…the EDRgen pipeline.

1. The image is taken by the HiRISE camera, and is stored in up to 28 channels, two for each of the 14 CCD arrays of the camera. Each channel covers about half of the image. Of the 14 CCDs, 10 are red CCDs, two are blue-green, and two are near-infrared. The color CCDs are aligned with the center red CCDs.
2. The image is placed inside a buffer on MRO, awaiting transmission to Earth, along with science data from the other instruments on MRO.
3. The image is received in packets by the Deep Space Network (DSN).
4. After 4 hours of collecting data at the DSN, the Jet Propulsion Laboratory (JPL) puts the packets together for what is known as a “quick look”. The entire image generally has not yet been received by this point in time, but it is enough of the image that it can be processed to take a quick look at it. Subsequently, JPL puts together all of the data it has received every 4 hours and makes it available to the computers at HiROC.
5. After the files have been put together by JPL, then one of the computers at HiROC looks and sees that there is data on the JPL server and copies the data to our system at HiROC. This is the start of what is known as the pipeline, the system of programs at HiROC which process the images. This usually happens either via a direct connection to JPL (slower), or through the Internet 2(Faster, but sometimes can be bogged down).
6. The images are put together into a viewable format, using the minimum processing possible, and create what’s known as an EDR, or Experimental Data Record. This is done without calibration, stitching together the channels, or any other processing, aside from putting the image together. For an image which uses all 14 CCDs, there will be 28 EDRs. These generally speaking are of mainly scientific interest, but they will be released to the general public via the Planetary Database System (PDS). They will be in the standard PDS format.
7. After the EDRs have been created, they are converted to another format for ISIS. ISIS, the Integrated Software for Imagers and Spectrometers is a suite of tools used for processing images for most interplanetary missions, that was developed by the United States Geological Society (USGS). Most of the tools that we use at HiROC for processing our images are written for ISIS files.
8. After the ISIS files have been created, they are calibrated via a program called HiCal. This reduces the inherent noise of the camera to be more consistent with what is being photographed. All digital cameras create some level of noise, and while HiRISE is an extremely good instrument, it still generates a low level of noise.
9. After the individual channels are calibrated, then they proceed to a program called HiStitch, which puts the two channels of the same CCD together. As they are a part of the same CCD, this requires little processing.
10. Next, after each CCD been stitched together, the full CCD images run through a program called HiccdStitch. This program puts the different ccds together, making a mosaic for each color band. This requires some processing, as the ccds slightly overlap, and it can sometimes be difficult to match the different arrays exactly.
11. If the image has not been completely received, then at this point, the pipeline stops, until JPL has received the entire image, or if there are a few confirmed gaps in the image which we haven’t been able to recover. Transmission over the vast distance between Earth and Mars is not easy, and even the best systems have some small error.
12. After the image has been completely stitched together, then the image is geometrically projected. To understand this, realize that the images that HiRISE takes are flat, while Mars is actually round. Geometrical Projection alters the image so that the image points in compass directions, while correcting any distortions that are created by the ellipsoidal shape of Mars. With the geometrical projection images and the right software tools, such as qview for ISIS, the exact distance can be found between two point on the image. In order for this to happen, we must wait for information to be gathered on the exact position of the spacecraft. This is done by the nagivational team, based off of the downlink frequency. This takes two weeks after the picture has been taken, so Geometric Projection might take a while. This is the longest wait point of the operation. An image can be released from predicted information, however, most images will wait for the correct SPICE kernels to be calculated, in order to get the best information. If an image is geometrically projected from predicted information, it will be calculated with the correct info after it has been received.
13. The images are then validated by a team of students known as the HiRISE Validators. They check to make sure that everything in the pipeline worked perfectly, see if there are any gaps in the images, and other similar tasks. If they notice a problem, they contact the HiRISE Operators, who will take steps to resolve the problems, which may include passing part or all of the image through the pipeline again, or tweaking the software to make it work perfectly.
14. The image is converted to a format that the general public can use. Currently that format is JPG, or TIFF, but eventually we will use JPEG 2000.
15. After all of this, the science team members of HiRISE will look at an image to see if there is anything noteworthy. If there is, it is given a caption, and perhaps a press release. If not, it will be posted on the HiRISE website. They are also posted on the MRO website, and occasionally on others.

This process may take as long as a week or two to complete, depending on the load of MRO, scheduling concerns, load at HiROC, etc. The first image took about 9 hours to be completely processed after it was taken by HiRISE. The Victoria Crater picture, taken during a much busier time on MRO, took about 36 hours to make its way to our hands. This was in part due to the larger size of the image, as well as the cache of images already awaiting transmission on MRO to earth. The captions for the images taken during Transition imaging took anywhere from a few hours to a few weeks to write, and this will likely continue to hold. We at HiROC want to release the images we take as fast as possible to the public, and we are doing everything we can to realize this goal. Several shortcuts were taken during the Transistion imaging phase that allowed for images to be released quicker. For Primary Science Phase, this will take a bit longer because these shortcuts will not be taken, but we expect that we will release most images within two weeks after them being taken, shortly after we have finished receiving, processing, and captioning the image.

There are some variations to this process, for example, the Victoria Crater picture was released in a press conference jointly with the Mars Exploration Rovers (MER) team. Also, color images require extensive calibration and take a lot more time. However, this is the general idea. Currently the entire system, except for writing the captions and adding the images to our website, is essentially completely automatic for receiving and processing HiRISE images, due to years of preparation by the HiTECH and HiOPS teams.