Another Day, Another Project: Identifying and characterizing all of Titan’s craters using Cassini’s COMPLETE data set.

I’ve another project to work on in addition to my original project studying the relaxation of Titan craters. If you’ve followed along, you’ll know there have been a number of issues trying to get the Fortran code to run and take the input files. Catherine doesn’t have a lot of background with it, and my collaborator is very busy with a number of other projects. Unfortunately, this has made for a very slow project. We aren’t casting it aside, but it’s being moved behind my new project of identifying and characterizing all of Titan’s craters. This has been done for most of Titan’s craters. However, we’ve now completed the final Titan flyby and have all the data we are going to have, so my task is to develop a systematic approach to search for all the craters that have been discovered and for any other possible craters. Then, I will use the topography data we have using Sartopo data to characterize crater size, depth and its other characteristics. Sartopo data is topography data obtained by calibrating overlapping radar flyby profiles that give the topography in the region where it overlaps.

I’ve begun by developing an easy system of functions to call the Sartopo data for a given crater. With the function ‘crater_elevation.m’ and the data file ‘sartopo_data.mat’ you can easily call the data profiles in the region by inputing the center latitude and longitude with the crater diameter.

For example, if we use the center lat and long of Menrva (425km) we’d put into matlab the following:

>> crater_elevation(19.6,87,425)

It returns a map of the region with the radar images overlain with a colorize height profile where ever there is sartopo data (Figure 1).

Figure 1: A map of the region of Menrva (lat: 19.6, lon: 87, 425km) with the a radar mosaic overlain with a colorized height profile where ever there is sartopo data. Height is in meters NOT kilometers.

A similar map is shown with each sartopo profile colored by profile number (Figure 2). This is derived from the sartopo data file names. SARTOPO_T00AS01_B12_V02_170315.CSV is 0000112, or 112 when inputed into matlab. Where the number is the fly-by (in this case fly-by A is 000), then the number after S and the number after B. The numbers after V are unchanging. The purpose of this plot is to just give perspective to where each profile is on the map.

sartopo map
Figure 2: A map of the region of Menrva (lat: 19.6, lon: 87, 425km) with the a radar mosaic overlain with sartopo profiles colorized by profile number.

All of the profiles are shown along the distance of their own profile track (Figure 3). You can use this to identify which profiles are of interest for further studying.

Figure 3: Each sartopo profile along the distance of the profile in km (x-axis) and the height of at each point.

The next step is identifying the crater depth and rim height and possibly width and height of central peaks/pits. I’m currently developing a code that will take the center lat and long and the crater diameter. It assumes you know the diameter, but I’m only using it to tell the code where to look for data. Once I’ve done that, I’ll go about finding where the rim is highest on each side, and the crater diameter is just the rim to rim distance. The function is still in development, but right now it also takes a vector of sartopo profiles that you want it to calculate the crater information for. I’ve added a step that allows the function to run without that defined. It will determine which profiles are inside 1 radii from the center lat and long and use these profiles.

If I make progress before the end of the day, I’ll add more info. The current plan is to find the center of each profile (from rim to rim of ~1.5 of the defined diameter) then look for the max height on either side. Then look for a point of flat lowlands between these two points. I suspect we may get profiles that run along the edge, so you may see a profile that forms like a V. I’ll try to develop a way to omit these profiles because it doesn’t map the inside of the crater. Another issue I’ll have to deal with is that the profiles don’t run through the middle. Even in Figure 2, profile 30112 doesn’t go exactly through the middle. The current idea is use the crater center thats given to the function and a bit of geometry to calculate the data for directly through the center. It’ll be interesting to see this done for a crater like Menrva where we have 4 solid profiles to do the calculation on.

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