Technique for correcting effects of long CO(2) laser pulses in aerosol-backscattered coherent lidar returns

Nondiffracting narrow light beam with small atmospheric turbulence-influenced propagation

A narrow light beam that propagates in the atmosphere with less disturbance than conventional light beams is introduced. The operating method and features of the newly proposed long-range nondiffracting beam (LRNB) are briefly demonstrated. Some experimental results of the atmospheric propagation of this beam at a distance of 500 m are shown in comparison with a conventional collimated beam and a focused beam. The results and related analyses show that the LRNB is much less influenced by atmospheric turbulence than other beams and suggest that the LRNB can apply to many fields.

Deconvolution of long-pulse lidar signals with matrix formulation

A deconvolution technique for deriving more resolved signals from lidar signals with typical CO(2) laser pulses is proposed, utilizing special matrices constructed from the temporal profile of laser pulses. It is shown that near-range signals can be corrected and small-scale variations of backscattered signals can be retrieved with this technique. Deconvolution errors as a result of noise in lidar data and in the laser pulse profile are also investigated numerically by computer simulation.

Remote measurements of vertical profiles of atmospheric constituents with a UV-visible ranging spectrometer

A study of the feasibility of retrieving vertical profiles of atmospheric constituents with a new UV-visible ranging spectrometer recently described by R. L. Jones [Optical Methods in Atmospheric Chemistry, U. Platt and H. I. Schiff, eds., Proc. Soc. Photo-Opt. Instrum. Eng. 1715, 393 (1992)] is presented. This instrument resembles a lidar, in that pulses of UV-visible radiation are transmitted vertically upward and backscattered to receiving optics. However, the pulse is a broadband source, and the receiving optics includes a two-dimensional CCD array that allows a series of absorption spectra to be recorded, each corresponding to a different altitude. This allows the simultaneous measurement of the vertical profiles of such atmospheric constituents as O(3), H(2)O, and NO(2) in the troposphere and lower stratosphere. Formal retrieval theory has been used to model the retrieval of vertical profiles with this instrument, demonstrating that it should be possible to obtain profiles at accuracies better than 30% and resolution better than 3 km up to altitudes of 12-15 km. The way in which the measurement error, flash-lamp pulse length, CCD recording interval, and mixing-ratio profile each affect the accuracy and the vertical resolution of the retrieved profile has also been investigated.

Water vapor absorption coefficients in the 8-13-microm spectral region: a critical review

Measurements of water vapor absorption coefficients in the thermal IR atmospheric window (8-13 microm) during the past 20 years obtained by a variety of techniques are reviewed for consistency and are compared with computed values based on the AFGL spectral data tapes. The methods of data collection considered were atmospheric long path absorption with a CO(2) laser or a broadband source and filters, a White cell and a CO(2) laser or a broadband source and a spectrometer, and a spectrophone with a CO(2) laser. Advantages and disadvantages of each measurement approach are given as a guide to further research. Continuum absorption has apparently been measured accurately to about the 5-10% level in five of the measurements reported. However, the effect of oxygen broadening has not been fully considered, since most laboratory measurements were made using nitrogen buffering. Oxygen could lead to a small reduction in the adopted value of the water vapor continuum absorption coefficient in air. Also, the temperature dependence does not seem to have been measured well for temperatures <20 degrees C. The rotational and v(2) line absorption coefficients do not appear to have been determined well in this spectral region except at CO(2) laser line frequencies, because the agreement between such measurements and the AFGL spectral data tapes is generally not good.