Lidar differential absorption, DIAL

Remote Atmospheric Monitoring.— Several techniques for remote atmospheric monitoring of pollutants, trace gases, etc. by LIDAR (Light Detection And Ranging) have become popular over recent years. Of these, DIAL (Differential Absorption Lidar) spectroscopy would seem to be of most interest to the... 

Various methods have been developed for remote gas sensing. These include differential optical-absorption spectroscopy (DOAS), differential absorption lidar (DIAL), and a number of methods that use spectroscopic methods with an atmospheric path in place of a laboratory long-path cell, for example tunable diode laser absorption spectroscopy (TDLAS) and Fourier transform infrared (FTIR) spectroscopy. 

The remainder of this article is devoted to the differential absorption LIDAR or DIAL method that is the most widely used technique for range-resolved remote gas sensing. It relies on elastic scattering from small particles and molecules that are always present in the atmosphere to return the signal. Speciation is achieved using the principle of differential absorption as described below. 

DIAL Differential absorption lidar PES Potential energy surface... 

DIAL differential absorption LIDAR, CAL compact aerosol LIDAR, //FT heterojunction phototransistors, PMT photomultiplier tubes, APD avalanche photodiodes Source Data from Refaat et al. (2003, 2011)... 

P. Weibring, H. Edner, S. Svanberg, G. Cecchi, L. Pantani, R. Ferrara, T. Caltabiano Monitoring of volcanic sulphur dioxide emissions using differential absorption lidar (DIAL), differential optical absorption spectroscopy (DOAS), and correlation spectroscopy (COSPEC). Appl, Phys. B 67, 419 (1998)... 

S. Svanberg Differential absorption lidar (DIAL). In Air Monitoring by Spectroscopic Techniques, ed. by M. Sigrist, (WUey, New York 1994)... 

A second form of LIDAR, known as Differential Absorption LIDAR (DIAL), uses two laser beams, one selected to be absorbed by a particular gas or vapor and a second as an unabsorbed reference. Pulses of the two lasers are then aimed and focused at a distant area through a telescope. Gas molecules in that area reflect some of both of the laser beams back to the telescope where they are detected and analyzed to determine if the gas or vapor of interest is present and, if it is, in what concentration. 

The requirements for very sharp and well-defined laser frequencies when using the DIAL teclmique can be relaxed by using a gas correlation lidar technique [10.108], where the back-scattered radiation from a broadband transmitter is split up in two channels one supplied with a cell filled with optically thick gas which only passes the off-resonance components for the signal, and one channel where the total signal (on and off) is detected. If the cell gas is present in the atmosphere, a differential lidar effect is obtained using many absorption lines simultaneously (compare Fig. 6.77). This technique... 

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