Aerosol and cloud backscatter at 106, 154, and 053 µm by airborne hard-target-calibrated Nd:YAG/methane Raman lidar

Abstract

A lidar instrument was developed to make simultaneous measurements at three distinct wavelengths in the visible and near infrared at 0.532, 1.064, and 1.54 mum with high cross-sectional calibration accuracy. Aerosol and cloud backscatter cross sections were acquired during November and December 1989 and May and June 1990 by the NASA DC-8 aircraft as part of the Global Backscatter Experiment. The instrument, methodology, and measurement results are described. A Nd:YAG laser produced 1.064- and 0.532-mum energy. The 1.54-mum transmitted pulse was generated by Raman-shifted downconversion of the 1.064-mum pulse through a Raman cell pressured with methane gas. The lidar could be pointed in the nadir or zenith direction from the aircraft. A hard-target-based calibration procedure was used to obtain the ratio of the system calibration between the three wavelengths, and the absolute calibration was referenced to the 0.532-mum lidar molecular backscatter cross section for the clearest scattering regions. From the relative wavelength calibration, the aerosol backscatter cross sections at the longer wavelengths are resolved for values as small as 1% of the molecular cross section. Backscatter measurement accuracies are better than 10(-9) (m sr)(-1) at 1.064 and 1.54 mum. Results from the Pacific Ocean region of the multiwavelength backscatter dependence are presented. Results show extensive structure and variation for the aerosol cross sections. The range of observed aerosol cross section is over 4 orders of magnitude, from less than 10(-9) (m sr)(-1) to greater than 10(-5) (m sr)(-1).

Tropical cirrus cloud properties derived from TOGA/COARE airborne polarization lidar

“…The airborne lidar used in this study was the NASA Goddard Space Flight Center Visible and Infrared Lidar (VIRL) system [Spinhirne et al, 1997], which is based on a Nd:YAG laser with a peak pulse energy of 150 mJ and a 50 Hz pulse rate. For the TOGA/COARE flights there were two linearly polarized 1.064 gm channels, plus 0.532 and 2.047 I•m total signal channels.…”

Method to Detect Molecular Ranges in Elastic Lidar Signal

“…It's important to remark that, because of the large degree of variability of real atmospheric situations, the shape of real lidar signals and its random noise makes it difficult to implement these concepts with an automated method [7]. Also, the application of the derivative or the variance to a lidar signal depends on the spatial resolution of the range-corrected signals [12], or in other cases, the definition of threshold values (like in [8], [9] or [15]). Limitations of derivative and variance method have been reported in [16], where different metrological situations could lead to fail in the detection of ABL height.…”

Airborne Instrumentation for Aerosol Measurements

“…Some examples are the large National Air and Space Administration (NASA) DC-8 airborne LIDAR systems, used by Browell et al, (37,38) McCormik et al, (39,40) and others, (41) which measured stratospheric aerosols, such as, for instance, the very early Pinatubo cloud, PSCs, tropospheric clouds, and aerosols. On the ER-2 a small compact LIDAR system was developed by Spinhirne and Hart.…”