R. Frehlich, SIMULATION OF COHERENT DOPPLER LIDAR PERFORMANCE IN THE WEAK-SIGNAL REGIME, Journal of atmospheric and oceanic technology, 13(3), 1996, pp. 646-658
The performance of coherent Doppler lidar in the weak-signal regime is
investigated by computer simulations of velocity estimators that accu
mulate the signal from N pulses of zero-mean complex Gaussian stationa
ry lidar data described by a Gaussian covariance function. The probabi
lity density function of the resulting estimates is modeled as a fract
ion b of uniformly distributed bad estimates or random outliers and a
localized distribution of good estimates with standard deviation g. Re
sults are presented for various velocity estimators and for typical bo
undary layer measurements of 2-mu m coherent lidars and also for propo
sed space-based measurements with 2- and 10-mu m lidars. For weak sign
als and insufficient pulse accumulation, the fraction of bad estimates
is high and g approximate to w(v), the spectral width of the signal i
n velocity space. For a large number of accumulated pulses N. there ar
e few bad estimates and g proportional to w(v)N(-1/2). The threshold s
ignal energy or average number of coherent photoelectrons per pulse wi
th accumulation is defined by a given fraction of random outliers and
is proportional to N--1/2 for large N and decreases faster than N--1/2
for small N. Ar the threshold level, the standard deviation g of the
good estimates is approximately constant fur large N. For space-based
measurements and with the signal statistics determined by the wind flu
ctuations over the: range gate, the 2- and 10-mu m lidars have similar
performance when referenced to the average number of photoelectrons d
etected per velocity estimate. The threshold signal level for large N
can be described by simple empirical functions.