The Southern Great Plains (SGP97) field experiment is being conducted in Oklahoma (see mission area) during June-July 1997. SGP97 is a NASA EOS Interdisciplinary Science Investigation to validate soil moisture retrieval algorithms at satellite temporal and spatial scales using remote sensing moisture measurements from aircraft and in situ soil measurements. The core experiment of the SGP97 is a remote soil moisture mapping L-band radiometer called ESTAR that operates from the NASA P3 aircraft. During the SGP97 observation period, it is planned, to map an area of about 15,000 sq km on a daily basis using ESTAR on the P3. One of the najor objectives of SGP97 is the study of the impact of soil moisture on the atmospheric boundry layer (ABL) development. To aid convective boundry layer (CBL) studies, LASE was deployed on the P3 along with ESTAR.
LASE (Lidar Atmospheric Sensing Experiment) airborne lidar, operates on the NASA P3 high research aircraft, and will produce measurements of aerosols and water vapor vertical profiles from the aircraft altitude (6-8 km) down to the surface. Such profiles show the vertical context in which the SGP97 in situ and radiometric measurements are made, thus supporting the vertical extension of the in situ measurements and detecting any unsampled layers or inhomogeneities, which would impact the surface and airborne measurements.
The LASE instrument is the first fully-engineered, autonomous DIAL (DIfferential Absorption Lidar) system for the measurement of water vapor, aerosols, and clouds in the troposphere. LASE uses a double-pulsed Ti:Sapphire laser for the transmitter with a 30 ns pulse length and 150 mj/pulse. The laser beam is "seeded" to operate on a selected water vapor absorption line in the 815 nm region using a laser diode with an onboard absorption reference cell. A 38 cm diameter telescope collects the back scattered signals and directs them onto two detectors and three signal digitizers with different gain settings. LASE collects DIAL data at 5 Hertz while onboard a NASA/Ames P3 aircraft flying at altitudes from 6-8 km. LASE was designed to meet the performance specifications provided by the DIAL water vapor instrument requirements, to operate autonomously, and to perform within the aircraft environmental and physical contraints. The LASE instrument was custom built and tested at NASA Langley Research Center in Hampton, VA. Additional information regarding LASE (descriptions, specifications, etc.), can be found in the cited references.
During SGP97, LASE was not operated when the P3 was below nominal altitude of 8.0km (~24000) feet. FAA regulations also required LASE to be turned off (laser beams blocked) during P3 turns and when optically thick clouds were present due to LASE eye safty.