A micropulse differential absorption LIDAR for temperature profiling

Abstract

This dissertation describes the development and testing of a Differential Absorption Lidar (DIAL) technique to retrieve temperature. This work showcases the accuracy of temperature retrievals using a perturbative technique, combining a DIAL measurement of a temperature-sensitive oxygen (O 2 ) absorption profile with a high spectral resolution lidar (HSRL) measurement of the backscatter ratio profile near 770 nm. This dissertation also introduces advancements to the DIAL temperature instrument and retrieval. First, the spectroscopic model used to represent absorption of light by O 2 has been enhanced, via a more complete physical representation, improving measurement accuracy. Second, the error estimation and masking have been developed using the bootstrapping technique. Third, a comparison of temperature profiles from the instrument with collocated radiosondes, evaluating the accuracy of updated measurements is performed. Finally, modeling of the lidar overlap function and atmospheric propagation and temperature retrieval allows for the modeling of sources of bias. A test of the DIAL temperature instrument was performed by NSF NCAR (National Center for Atmospheric Research) in Fort Collins CO in 2021. The data were collected between June 17 and August 20, 2021. Radiosonde comparisons were available for comparison. Results show temperature comparisons with radiosonde that have a bias of about 1 oC and a standard deviation of about 3 oC. Another test of the DIAL temperature instrument was performed at Montana State University. The laboratory-based lidar instrument was operated over a six-month period between April 21, 2022 and September 22, 2022. During this time, we launched 40 radiosondes, providing reference data to validate the accuracy of the DIAL-based temperature profiles. The results indicate that DIAL-based temperature retrievals are within + or - 2.5 oC between 0.4 km and 3 km (3.5 km) range during daytime (nighttime) operation, using a 300 m range resolution and a 60 min averaging time.