Context Navigation

FWMikesNotes

v10	v11
30	30
31	31	The FWD records either 64, 128 or 256 samples. These 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). This will also help capture (for example) sparse tree tops prior to the first return.
	32
	33	''Additional info from emails circa 4/July/2010'': It appears the hardware supports 512 samples and down to low as 15.26k samples/second (6500 nanoseconds), or roughly 10,000m. As such, the full distance to the ground can be digitised. One would have to be careful not to set the digitisation so long that it receives a second pulse while still digitising the first.
32	34
33	35	The intensity is digitised to an 8 bit value. This is measured after the AGC amplification has taken place and is nominally the same measurement as in the discrete system (though the discrete value is accumulated over a longer time period so will typically have a higher value). The AGC value for the matching discrete return is the value used for all the related FWD samples - i.e. the AGC value is constant for a laser pulse.