Pergamon Atmospheric Environment Vol. 28, No. 2, pp. 257-264, 1994 © 1994ElsevierScience Ltd Printed in Great Britain. All rights reserved 1352-2310/94 $6.00+0.00 A LIDAR TECHNIQUE TO QUANTIFY SURFACE DEPOSITION FROM ATMOSPHERIC RELEASES OF BULK LIQUIDS MADISON J. POST a n d THOMAS GLAES NOAA Wave Propagation Laboratory, 325 Broadway, Boulder, CO 80303, U.S.A. JOSEPH MATTA ~ a n d DOUGLAS SOMMERVILLE U.S. Army Chemical Research, Development and Engineering Center, Aberdeen Proving Grounds, MD 21010, U.S.A. and WAYNE EINFELD Applied Atmospheric Research Division, Sandia National Laboratory, 1515 Eubank Avenue, Albuquerque, NM 87123, U.S.A. (First received 12 March 1993 and in final form 29 June 1993) Abstract--We show that a scanning, pulsed lidar can be used to quantify the time history and areal concentration of mass deposited on the ground from an elevated release of bulk liquid. Aircraft measurements, witness card depositions and evaporative modeling crudely support results from analysed lidar data. Key word index: Lidar, dispersion, spraying, deposition. INTRODUCTION Between 5 and 23 August 1991 the U. S. Army Strategic Defense Command (SDC) Theater Missile Defense Bulk Chemical Experiment (TMDBCE) con- ducted a series of unclassified experiments at Dugway Proving Grounds (DPG) in central Utah. The purpose of the tests was to determine the feasibility of using a suite of sensors to measure the dispersion and surface deposition of clouds of thickened tricthyl phosphate (TEP) for a series of tests to be conducted at White Sands Missile Range (WSMR) in New Mexico in the following years. At DPG the TEP was explosively disseminated at altitudes above ground from 200 to 4000 m. TEP possesses physical properties similar to several chemical warfare agents held by potential adversaries. Among the objectives of the test program at WSMR is to determine the minimum altitude for intercepting offensive missiles (such as the Scud mis- siles of the recent Middle East war) to ensure that their liquid payload is rendered ineffective through disper- sion and evaporation. The lidar technique used during these tests serves equally well in measuring elevated atmospheric releases of any liquid substance that experiences aerodynamic breakup, such as agricul- tural products sprayed from aircraft or fire retardants dropped near forest fires. Previous lidar work for similar applications has been substantial (see Heft et al., 1989), but it has concentrated primarily on sprays of smaller droplet size released from aircraft at shorter ranges and lower altitudes. At DPG 55-gallon (0.208 m 3) drums of TEP were raised in pre-dawn hours to a pre-set test altitude by a helium-filled tethered balloon for detonation about 1 h after sunrise. This strategy was chosen to minimize the effects of post-sunrise changes in the nearly con- stant southeasterly nocturnal drainage winds at DPG, and to avoid complications from midmorning convec- tive turbulence that typically began about 3 h after sunrise. The balloon's anchor vehicle and wrench were moved prior to each test by the crew from the Air Force Geophysics Laboratory (AFGL) to try to make the TEP fall near the center of a multiple impact (MI) grid of sample cards. The grid covered an area of 5000 x 5000 m, with a grid spacing of 100 m (except in the center 400 x 400 m, where the spacing was 25 m). The cards, each about 20 cm square, were designed to capture an imprint of liquid droplets that reached the ground, in order to measure the droplet size spectrum and to calculate total mass deposition. After readiness checks and a countdown, the drums were exploded with an embedded charge of C4 explosive, whose detonation was triggered remotely via radio. Two lidars, an incoherent Nd:YAG system oper- ated by DPG staff and a coherent CO2 system operated by National Oceanic and Atmospheric Ad- ministration (NOAA) personnel, then mapped the cloud boundaries and tracked the cloud as it advected 257