Abstract

Tunable diode laser (TDL) sensors for atmospheric measurements possess many advantages including wide tunability in the infrared where most atmospheric species possess strong absorption bands; high spectral resolution which yields high specificity and sensitivity for the detection of clean air levels of trace gas species; and fast time response that is necessary for making gas flux measurements using the eddy correlation technique. A NASA Langley developed airborne TDL sensor has participated in several major atmospheric measurement programs since the late 1970s. This presentation focuses on measurements with this sensor on the NASA Electra aircraft during the Global Tropospheric Experiment (GTE) expeditions to the Amazon forest (spring 1987 wet season) during which CO measurements were made and to Alaska (summer 1988) during which simultaneous CO and CH₄ measurements were made. This TDL sensor possessed a time response of ≈70 ms which was sufficient to spatially resolve the turbulent eddies which are responsible for the vertical transport of gases emitted from the earth′s surface. By correlating rapid measurements of gas concentration with vertical wind velocity data provided by a gust boom, direct measurements of gas flux were made. Data from these expeditions have quantified CO emission by the Amazon tropical forest and CH₄ release over Alaskan tundra environs. Since CO and CH₄ have key roles in the green-house process, flux data of these species are important for making improved estimates of global gas budgets and as inputs to atmospheric computer models.

© 1989 Optical Society of America