CALIPSO Lidar Calibration at 532 nm: Version 4 Daytime Algorithm

Abstract

Abstract. The Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission released 10version 4.00 of their lidar level 1 data set in April of 2014, and subsequently updated this to version 4.10 in November of 2016. The primary difference in the newly released version 4 (V4) data is a suite of updated calibration coefficients calculated using substantially revised calibration algorithms. This paper describes the revisions to the V4 daytime calibration procedure for the 532 nm parallel channel. As in earlier releases, the V4 daytime calibration coefficients are derived by scaling the raw daytime signals to the calibrated nighttime signals acquired within a calibration transfer 15 region, and thus the new V4 daytime calibration benefits from improvements made to the V4 532 nm nighttime calibration. The V4 calibration transfer region has been moved upward from the upper troposphere to the more stable lower stratosphere. The identification of clear-air columns by an iterative thresholding scheme, crucial to selecting the observation regions used for calibration, now uses uncalibrated 1064 nm data rather than recursively using the calibrated 532 nm data as was done in version 3 (V3). A detailed account of the rationale and methodology for this 20 new calibration approach is provided, along with results demonstrating the improvement of this calibration over the previous version. Extensive validation data acquired by NASA's airborne high spectral resolution lidar (HSRL) shows that during the daytime the average difference between collocated CALIPSO and HSRL measurements of 532 nm attenuated backscatter coefficients is reduced from 3.3% ± 3.1% in V3 to 1.0% ± 3.5% in V4.

Improved Hydrometeor Detection Method: An Application to CloudSat

“…Here, the resulting cloud mask using the improved hydrometeor detection from G17 (described below as the G17 version) is compared with the operational CloudSat R04 and R05 version cloud masks, which are stored in level 2B GEOPROF data products. Following M08, we use the CALIPSO version 4 lidar vertical feature mask (VFM) (Getzewich et al, ; Vaughan et al, ) as a reference to evaluate hydrometeor detection algorithm, because the lidar is more sensitive to thin cloud than the radar. For most of their operational life (and for all the data examined here), CALIPSO and CloudSat were both parts of the A‐Train satellite constellation.…”

Application of High-Dimensional Fuzzy K-means Cluster Analysis to CALIOP/CALIPSO Version 4.1 Cloud-Aerosol Discrimination

“…The improved calibration coefficients in V4 facilitated the detection of optically thinner layers than were detected in V3 Getzewich et al, 2018). A side effect of this improvement is an increased occurrence of optically-thin layers detected along the tenuous edges of ice clouds.…”

authors' response to referee #1

“…Recent studies have found higher lidar ratios for volcanic ash (Table 3). For example, lidar ratios of 50 ± 10 sr were retrieved for volcanic ash transported over Europe during the April 2010 Eyjafjallajökull volcano eruption Groß et al, 2012), with mean lidar ratios of 60 ± 5 sr at Leipzig on 16 April 2010 . Recently, Prata et al (2017) used constrained CALIOP retrievals to estimate mean particulate lidar ratios of 69 ± 13 sr for volcanic ash from the June 2011 Puyehue-Cordón Caulle eruption.…”