Calibration of 1064 nm channel of LITE using playa surface returns

The Lidar In-space Technology Experiment (LITE), the first NASA spaceborne atmospheric lidar yielded data on atmospheric aerosols and surface reflectance. The IR 1064 nm channel did not have a sufficiently strong Rayleigh backscatter to enable calibration off the molecular atmosphere as did the 532 nm and 355 nm channels, so surface returns were considered for calibrating the IR channel. The uses of LITE surface returns have been investigated with related laser altimeter measurements from the Race Track playa in Death Valley, CA examined by these authors in preparation for the LITE mission. The LITE surface returns from Rodgers dry lake are compared with the previous measurements. Two approaches of calibrating the IR channel are considered. First, the reflected signal variance is determined for calibration of the 1064 mn channel surface returns off the playa. This requires that the ratio of the reflectance between the green and IR channels be known from an additional data source. Passive reflectance measurements were made of the playa to establish this ratio with a non-backscatter geometry which adds to the uncertainties of the result. The second approach is to calibrate using the absolute value of the 1064 nm backscatter reflectance. This can be inferred from passive measurements and modeling of the playa angular reflectance characteristics. The effects of errors introduced by the lidar system, correlative optical depth measurements and surface reflectance measurements and modeling are considered to obtain the 1064 nm channel final calibration error margin using both reflectance calibration approaches. The basic lidar relationships are reviewed, and the error dependencies in the lidar equation are discussed as they apply to the LITE surface returns