Evaluation of a Perturbative Retrieval Technique for Temperature Profiling in the Lower Troposphere Using Differential Absorption Lidar (DIAL)

Thermodynamic profiling, including measurements of absolute humidity and temperature in the lower troposphere, can help define the state of the atmosphere and can provide important information for many atmospheric science and weather forecasting applications. A collaborative research effort between Montana State University and the National Center for Atmospheric Research has led to the development of diode-laser-based micro-pulse differential absorption lidar instruments to address the need for networkable remote sensing instruments for thermodynamic profiling of the lower troposphere capable of long-term unattended operation.

Recent research efforts include the development of a differential absorption lidar (DIAL) instrument that combines the ability to monitor a temperature-sensitive absorption feature of O₂ using a DIAL measurement along with the ability to monitor the backscatter ratio (the ratio of the total backscatter to molecular backscatter) based on a high spectral resolution lidar measurement. A recently developed perturbative retrieval combines the O₂ absorption and backscatter ratio profiles to retrieve the temperature profile.

This presentation will focus on the capability of the DIAL instrument, along with the perturbative retrieval of the temperature profiling, to measure temperature in the lower troposphere. The DIAL instrument was operated between April and September 2022. Over this time period, a total of forty co-located radiosondes were launched. Comparisons of the temperature profiles retrieved from the DIAL instrument using the perturbative temperature retrieval to the temperature profiles measured with the radiosondes were used to evaluate the ability to measure temperature in the lower troposphere. The comparison of the DIAL-based temperature retrievals and the temperature profiles measured using the radiosondes indicate that DIAL-based temperature retrievals are accurate within ±2.5 ^oC between 0.4 km and 3 km (3.5 km) range during daytime (nighttime) operation, using a 300-meter range resolution and a 60-minute time resolution.