The gas sensorat station 5 was a miniature, rapid-response, infrared system prototype that we developed for DOE and modified to detect methane.° It operates on the principle of differential absorption of infrared radiation by various gases. Onefilter allows infrared radiation of a wavelength heavily absorbed by methane to pass, and another gives us an unabsorbed wavelength. By comparing the intensities of the two beamsafter they have passed through the gas, we can calculate the methane concentration. The infrared sensor was the only truly portable instrument used in thesetests. It operated well in environments with temperatures ranging from ~20 to +40°C.Its measurement capabilities were essentially independent of the presence of water vapor, droplets, or dust in the absorption ceil. Stations 7 and 8 had, in addition to the usual grab samplers and sight that extended through the gas and 6 are 2.1 m,station 4 is 1.5m, plume. It used a pulsed laserto ex- and station 3 is 0.6m above the pond surface. Stations 1 and 2 are cite the gas and then measured time-gated Raman-scattered return on the pond. The laser beam of the LIDAR was about 2m above the signals from the 9-m-long range surface of the pond. gates shown in Fig. 1. At each of stations ] through 8 there was a thermocouple, a grab Atmospheric transport sampler, and a gas sensor measur- modeling In each experiment, we used the ing conditions at a standard height atmospheric transport model of 0.9m above the ground. Most stations had an auxiliary therATMAS* to aid in the analysis of mocouple at 0.6 m. Stations 3 and _the measured concentration data. 6 were more complex, with towers The ATMAScode is a threedimensional computer model that 4.5m tall carrying thermocouples at the top and at 3.6, 2.4, and we developed to predict the 1.5m. There was also a grab sam- transport of pollutants entering the atmosphere from extended or mulpler, gas sensor(TSI), and thermocouple at 2.4 m, and a separate tiple sources. One of its major grab sampler and thermocouple at capabilities is that of simulating a three-dimensional, time-varying 0.45 m. wind field from wind data obtained Because the ground rises immediately downwind from the spill at different points within the region of interest. A time-varying windpond, stations 7 and 8 are 6m above the pond surface. Stations 5 field model is much morerealistic thermocouples, Mine Safety Ap- pliances (MSA) gas sensors. These sensors used a filament covered with a catalyst (to promote combustion} together with a means of measuring the heat evolved. They detected gas only up to the stoichiometric concentration (10 vol% for methane). The LIDAR instrument, used only in the second test of the series, — operated remotely over a line of Talolle Jl A summary of the 5-m7 LNGspill tests at the Naval Weapons Center, China Lake, California. Test number 1 2 3 Date Time Temperature, °C Relative humidity, % Spill volume, m° Spill duration, s 31 Aug 14:56 35.8 16 4.39 67 13 Sept 19:37 21.1 29 4.52 59 9 Nov 15:26 26.8 15 4.5 77 20 Nov 15:11 20.1 21 4.2 32 Spill radius, m Boiloff time, s 7.22 90 7.81 80 6.82 85 Variable 120 Source rate, kg/s 20.58 93.84 22.34 4 44.0 (g/m?-s)