Changes between Version 3 and Version 4 of Sensors/LeicaLIDAR/FWMikesNotes

Timestamp:

Jan 27, 2010, 6:58:33 PM (15 years ago)

Author:

mggr

Comment:

--

Sensors/LeicaLIDAR/FWMikesNotes

@@ -12 +12 @@
 }}}
 
-The FWD i
+The FWD is implemented as two sampling boards
+
+The FWD digitises the incoming intensity level and nothing else.  It records either 64, 128 or 256 samples at 1 or 2 nanosecond resolution (1ns is approximately 15cm). The samples are recorded from the time of the first return, with a small buffer before that (the "pre-trigger samples").  This buffer allows the capture of the lead-in to the first pulse (otherwise it would start at the first detected peak) and is specified in terms of meters to the operating software (default 5m).
+
+Processing note: the trigger from the discrete system appears to have a small delay (order of 7ns?), that is different for the two possible laser pulse rates and also may be dependent on temperature (unproven).  This delay manifests as an offset between the discrete returns and the matching waveform peaks.  At the time of writing, it is corrected by a manual / statistical approach (see below).
 
 
+Some other important points:
   * Nothing has changed for the AGC/mainboard of the ALS so the raw laser .SCN files will be the same as before. 
   * Extra files will be created that contain the waveform data. Waveform files (.LWV) will be in the raw_wfd directory, SCN files in the raw_laser directory.