My current favorite lunar imagery tool is Arizona State's Lunar Reconnaissance Orbiter site. (Sorry LMMP.) It has a section where you can search for imagery by filling out a form, which is great because little did I know most of the Moon has been imaged many times now by various instruments, and sorting through them on their map is difficult, no matter how great the interface is.

'this search returned 3174848 results'

But alas, it is still pretty confusing to a lay person.

LROC image search form

What do the different angles mean? I think what I want is photos with a high slew angle, looking more towards the horizon and less downwards, but I'm not sure. Wouldn't that be the same as incidence angle? I also don't understand sub-solar azimuth or latitude. Or orbit.

I have sorted out that observation type is 'narrow angle' for the ones that start with NA, but don't get the difference between CL and CR. WA is wide angle, and is color, monochrome, ultra-violet, and visible - but wouldn't visible be the same as monochrome?

If people haven't looked at this imagery, I wanted to include a little sample of how detailed it can be now. This is a small bit of the central peak of Tycho Crater:

boulders and strata on peak of tycho crater


1 Answer 1


These are standard terms used by the Planetary Database System. MSSS provides some explanations of these terms.

  • Product ID- Each product (image) has a unique id, if you know the exact image, put this one in.
  • Coordinate Range- Range to the coordinates from the spacecraft.
  • Incidence Angle- This is the angle that the sun is to the surface. A low angle means the sun is straight overhead.
  • Emission Angle- This is the angle of the point on an image to the perpendicular of the spacecraft. Straight down is 0 degrees, higher means off-angle imaging.
  • Slew Angle- Similar to Emission Angle, but the Slew is the off angle pointing for the spacecraft, while Emissions is the off angle at a particular point. Most of the time these will be very close to each other.
  • Resolution- Resolution of image
  • Exposure- How long the exposure was of the image (How long did it take to make the image)
  • Sub-Solar Azimuth - This is the angle of the sunshine on the image, measured from 0 at the right hand size of the image. If 0, the sun is coming from the right hand size, etc.
  • Sub-Solar Latitude- This is the latitude on the object where the sun is shining directly overhead. On Earth this would vary between +- 23, for instance, depending on the time of year, other objects have different ranges.
  • Orbit - What orbit number the image was taken
  • Observation Date- Date of the observation

In your case, you probably care the most about the Slew Angle and the Incidence Angle.


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