J Weirich conversed with R Gaskell on Feb 13, 2017

This is only relevant for v3p1 and albedo.f. If you are using this version, it would be prudent to include these parameters in INIT_LITHOS.TXT. I tried just switching over to the v3p1 software with the same INIT_LITHOS.TXT I used for v3p0 and things went unstable.

There is a line required in INIT_LITHOS.TXT and for albedo.f called TPARS. It looks like this.

TPARS= 1.D0 1.5 .05 1 2 6 0 0 0 0

1st: If the image "resolution" (really the image resolution / maplet resolution) is that value or worse, than the image is de-weighted. Typically the image "resolutions" will be between 0 and 3, this parameter will let you include low res images for better stereo, but won't weight those images much when building topography. Typical value is 1.

2nd: This value determines the spread of albedo values that will exist in the maplet. 1.0 is typical and will do the standard scaling of albedo between 0 and 2. If using albedo.f you will ALWAYS use 1.0. If you are using LITHOS than a good value to use is 1.5, which will make the spread more narrow. Bob says this is useful when performing iterations since it will keep the albedo from doing crazy things while the topography is warping to the proper place.

3rd: The brightness of a pixel is between 0 and 1. This parameter will de-weight a pixel with a brightness value less than this value. Typically we use 0.05, so if a pixel brightness is less than 0.05 it will de-weight the pixel in that image. I think this helps with shadows and the like.

4th: Bob was testing something but didn't like the results it was producing. Set it to 1 and don't ever change it.

5th: This will de-weight images that have low phase. The value is the phase angle in degrees. So a value of 2 will de-weight all images less than 2 degrees. Typical value is 2.

6th: This value is how many standard deviations away you let the solution wander. So 6 would be 6*STDEV. In LITHOS, pixels won't be allowed to change further than that value from the average. In albedo.f if the pixel values is greater than the X*STDEV, then it just doesn't use it.

7th through 10th are currently not used but are there for future debugging. Currently they should just be set to 0 (zero).

For albedo.f, you need a file called ALBEDO.TXT. I think you a line that has the TPARS line (though without the TPARS=) another line below TPARS that has four parameters.

Asig typically set to .05

etol typically set to .025

L0 ???

N0 Typical value is 4. This means that if there are less than 4 images for a specific pixel, the albedo value for that pixel is set to 1.

The ALBEDO.TXT file should, I think, look like this...

1.D0 1.5 .05 1 2 6 0 0 0 00.05 0.025 30 2

X.LITHOS

There is a version of albedo.f called ALBEDOX.f; currently in X-files/source/. This needs to be tested more, but preliminary testing shows it runs using similar criteria as albedo.f.