Earthdata Forum

Hi, all,

I have read and checked numerous product handbooks from this website: "https://gedi.umd.edu/instrument/instrument-overview/", and also published papers, but fewer of them specify GEDI system configuration and operation parameters.

What I want to know includes following parameters:

1) RMS width of receiver impulse response (unit: nanosecond)

2) half width of divergence angle of laser beams (unit: degree). This website: "https://gedi.umd.edu/instrument/specifications/" says that GEDI beam laser divergence angle is 56 mrad, which is much larger than ICESat GLAS, generally between 0.11 and 0.17 mrad, is it reliable?

3) off-nadir point angle of laser beam (unit: degree). This website: "https://gedi.umd.edu/instrument/instrument-overview/" hints that GEDI minimizes its off-nadir pointing to be less than about 6° to avoid inaccurate range measurements, it there any normal averaged value, like 3°?

4) laser beam inclined angle (unit: degree).

I would appreciate it if anyone tell me some info about these.

Cheers,
Jw

Hi @ljw6413 Thanks for writing in. We are checking with the GEDI Science Team on answers to your questions. We'll reply when we have an answer. Please note responses may be delayed due to the holiday season. Thanks!

Thanks for your reply and please forgive me for late response. I am awaiting your response. Thanks again!

Hi @ljw6413 We are still waiting to hear back, with the holidays and staff schedules we might not get an answer until after the new year. We apologize for the inconvenience.

Hello,

We did hear back from the developers on this, please see the following: There’s basically no “typical” pointing angle – we’re dependent on what the ISS is doing at any one time, which I think has included going up to like 10deg in pitch at one time.
GEDI as an instrument has the ability to move its pointing across track (roll) by +-6deg - which when combined with the ISS pointing, allows us to point to appropriate RGT’s to build up coverage, or to target cal/val sites - but that +-6deg has to be considered with the ISS roll angle (and pitch). GEDI may not even be able to fully compensate for whatever roll the ISS is doing (and it cant compensate for pitch).

Local_beam_elevation is as close as we have to a pointing angle in the data (its in l2a and l2b aswell as l1b – as in its just repeated in the l2’s). Theres local_beam_azimuth to give the azimuth also. We basically try to keep the GEDI pointing as close to nadir as we can, whilst building up coverage, but ultimately are subject to whatever ISS is doing.

Thanks, and plaes let us know if you have any questions.
Brett