Earthdata Forum

The LP DAAC User Services team received the following question via email. We believe the answer will help the science community, so we are adding it to the forum too.

From a user:
At the risk of interrupting, I would like to ask a question about GEDI data.
I am a student. I read GEDI L1B data in R language and found that the
"rx_energy " value of multiple shot_number of a certain data of L1B raw data is negative, is this because of noise or because this is an outlier in the
raw data? I would be especially grateful if you could get back to me as soon
as possible!
shot_number latitude_bin0 latitude_lastbin longitude_bin0
longitude_lastbin elevation_bin0 elevation_lastbin tx_egamplitude rx_energy
1: 40270000100000001 -29.76426 -29.76426 -88.13303
-88.13303 6656.992 6642.007 0 -49.7500
2: 40270000100000002 -29.76407 -29.76407 -88.13283
-88.13283 6656.312 6641.327 0 25.0000
3: 40270000100000003 -29.76388 -29.76388 -88.13263
-88.13263 6656.232 6641.247 0 -138.1875
4: 40270000100000004 -29.76370 -29.76369 -88.13242
-88.13242 6656.751 6641.766 0 70.9375
5: 40270000100000005 -29.76351 -29.76351 -88.13222
-88.13222 6656.670 6641.685 0 -70.4375
6: 40270000100000006 -29.76332 -29.76332 -88.13202
-88.13202 6655.990 6641.005 0 -64.5000

These are noise-only returns. Probably tracking over clouds and unable to get to the ground, so the shot has used the parameters of the last shot in which signal was detected to locate the return waveform. The user can use "quality_flag" and if it's 1, then it passes some initial checks on whether the shot is usable. They can also look at elevation_lastbin or elevaiton_bin and see if they fall within the range of a dem (in this case, they are all around 6650m over the ocean).