A paper describes the Microwave Temperature Profiler (MTP) for making measurements of the planetary boundary layer thermal structure — data necessary for air quality forecasting as the Mixing Layer (ML) height determines the volume in which daytime pollution is primarily concentrated. This is the first time that an airborne temperature profiler has been used to measure the mixing layer height. Normally, this is done using a radar wind profiler, which is both noisy and large.
The MTP was deployed during the Texas 2000 Air Quality Study (TexAQS- 2000). An objective technique was developed and tested for estimating the ML height from the MTP vertical temperature profiles. In order to calibrate the technique and evaluate the usefulness of this approach, estimates from a variety of measurements during the TexAQS-2000 were compared. Estimates of ML height were used from radiosondes, radar wind profilers, an aerosol backscatter lidar, and in-situ aircraft measurements in addition to those from the MTP.
Relative to the benchmark radiosonde estimates, radar wind profiler ML height estimates were nearly bias-free. Airborne lidar and profiler estimates generally were in good agreement inland, but spatial gradients of ML heights made comparisons difficult near the coast. The presence of a residual layer above the sea breeze was probably responsible for a gross overestimate of ML height by lidar in a few instances. The accuracy of the MTP-based ML height estimates is similar to that of other techniques for estimating ML height. The airborne MTP thus shows promise for measuring the spatial distribution of ML structure, especially in coastal environments where aerosol lidars may have difficulty identifying the ML.