W. Wiesemann’s research while affiliated with Battelle Memorial Institute and other places

A multispectral DIAL has been developed to accurately identify and quantify gaseous pollutants in the troposphere. The lidar uses the multispectral differential absorption technique and consists of a CO2 laser operating in the 9-11 micron region with a maximum repetition rate of 300 Hz, a rapid tuning device as the transmitter, and a telescope with a liquid nitrogen cooled HgCdTe-detector as the receiver. The measurement principles, basic instrument design, and hardware status of the instrument are summarized.

The proposed airborne remote sensing instrument known as the Lidar Multispectral Earth Observation System (Limes) is described. The Limes is a combination of an imaging 4-channel laser spectrometer operating in the 9.1-11.2 micron range and a 11-channel multispectral scanner operating between 0.42 and 13.0 microns. The technical aspects and characteristics of the Limes are presented. The geological and geophysical applications of the system are outlined and a simulated spectroscopic image is presented to demonstrate the concept of Limes data displays.

A transportable laser system for remote sensing of road traffic emissions (carbon monoxide) has been developed and field testet at different sites in the city of Frankfurt. Based on the DAS technique using lead-salt diode lasers, the system yields mean values of the species density across a measurement path of several hundred meters. Interference with other absorbing species as well as varying operating conditions are compensated by using the second derivative technique. The time for starting operation after transportation of the system was two hours, time of availability during the campaign was better than 90%. It appeared sufficient to have technical checks and readjustments only once per day.

Remote measurements of trace species with a cw CO2 DIAL system suffer from errors caused by unknown variations of the target reflectivity with wavelength. Information on the mineral content of the ground gained by an airborne four-wavelength CO2 DIAL system can be used to correct remote trace species measurements performed by the same apparatus. Reflectance data in the CO2 laser spectral region for various rock and soil types are presented. The mineral content was determined by x-ray analysis. The technical performance of a two-wavelength airborne CO2 DIAL system was field tested by different methods, such as correlation techniques and comparison of target reflection data taken in the laboratory, and by remote measurements.

The application possibilities of thermal infrared laser spectroscopy for remote sensing were investigated in laboratory and flight campaigns. For the flight measurements, a profiling laser spectrometer with 2 tunable CO2 lasers was used. In the laboratory, the reflection spectra of minerals, soils, rocks, vegetation, water, moistened surfaces and oil spills on water were taken. Flight measurements (soil, rock surfaces, water, irrigated field, vegetation, asphalt) agree with the laboratory results (in-situ measurements). Based on these results, a program for the development of an optical multisensor, combining mid IR laser scanner and near IR-multispectral scanner was started.

Differential albedo and absorption measurements indicate the feasibility of remote detection of minerals, soil moisture, oil-spills and atmospheric trace gases. Laboratory measurements and results from several flight campaigns with a coherent CW CO2 laser sensor are reported.

Airborne remote sensing systems using the earth's surface as a reflector are suffering from the differential reflectance properties of the topographic targets. For example, the errors associated with ozone monitoring in the thermal infrared can reach up to 70 ppb.km ¹⁾ . This paper proposes a scheme which can reduce this margin remarkably, however, on the penalty of increased technical complexity.

The application possibilities of active infrared spectroscopy to remote sensing of soil and rock types and surface soil moisture was investigated in laboratory work and flight campaigns. For the flight measurements the DIALEX instrument, a profiling laser spectrometer with tunable CO2-lasers (9 to 11 microns) was used. The differential reflection data of flight measurements agree with laboratory results. The mean deviation between these data is 15%. Especially for large homogeneous test sites like grass land, ploughed fields and lake Ammersee the mean deviation is 15%.

The design of CO2 laser transceiver system to establish and maintain a two way 1 Gbit/sec data link between two independently orbiting satellites is presented. The overall package has envelope dimensions of 70x35x90 cm, weighs 37 kg, and consumes 250 W of prime power. It comprises an externally modulated CO2 laser transmitter, an optical homodyne receiver, diffraction limited transceiving optics, a high performance pointing acquisition and tracking subsystem, and a stable light weight mechanical structure. Operational procedures are discussed and calculated performance data are given.