On the Development of Long-term Climate Benchmarks from Satellite Lidars
by Dr. David Winker, Dr. Hélène Chepfer

Abstract

Held in 2006, just a few weeks after the launch of CALIPSO, the report of the Achieving Satellite Instrument Calibration for Climate Change (ASIC3) Workshop included a few preliminary thoughts on calibration needs for active instruments for climate applications. The inherent sensitivity of lidar for cloud detection and inherent accuracy of cloud height and cloud thermodynamic phase measurements was identified, along with the potential for the construction of long-term benchmark time series from satellite lidars. The CALIPSO mission has now completed its 16th year on-orbit and global cloud climatologies have been produced from CALIOP observations. CALIOP observations have been used extensively to evaluate cloud products from passive sensors and formed an important part of the GEWEX Cloud Assessment. But to treat the CALIOP cloud products as climate benchmarks requires identification and quantification of uncertainty and biases. One must also ask what 'traceability' means for satellite lidar observations and which variables are suitable for benchmark data records. CALIOP cloud products have been extensively used to evaluate the representation of clouds in global climate models but to fully evaluate climate models requires multi-decade data records. CALIOP has been followed by the ALADIN wind lidar and we look forward to the launch of EarthCARE with the ATLID lidar. Each of these instruments have significant design differences from CALIOP and the construction of long-term climate data records spanning multiple satellite lidars requires consideration of differences in orbit and instrument characteristics. We will present current approaches to lidar calibration and preliminary thoughts on what is involved in achieving stable, traceable observations from satellite lidar and on devising instrument guidelines to promote the development of long-term benchmark data records.