Date of Award

7-2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean Engineering and Marine Sciences

First Advisor

Steven Lazarus

Second Advisor

Michael E. Splitt

Third Advisor

Pallav Ray

Fourth Advisor

Nezamoddin Nezamoddini-Kachouie

Abstract

Despite the increasing availability of weather products and access to data, the issue of weather representativeness, especially in relation to terrain, persists in the aviation industry. Data-sparse regions pose a particular challenge, requiring focused research efforts to address this issue and reduce accident and fatality rates within the general aviation (GA) community. This thesis aims to tackle the specific problem of representing visibility conditions, with a focus on obscuration conditions in elevated terrain.

To achieve this goal, data from Automated Surface Observing System (ASOS) ceilometers and nearby mesonet relative humidity (RH) were analyzed to establish a relationship between the lowest broken or overcast layer (ceiling) detected by the ceilometer and the RH of mesonet stations in nearby terrain. To account for different climates and topography, two regions of interest were selected for this study: Northwest Los Angeles (LA), with an emphasis on the Calabasas region, and the Great Smoky Mountains (GSM).

Archived camera imagery provided by the National Parks Service (NPS) at two of the NPS-run mesonets (Look Rock and Clingmans Dome) in the GSM region was utilized to determine the presence of obscuration conditions when ceilings and high RH were detected at the mesonet. This verification was necessary as RH is not a perfect indicator for the existence of an obscuration. A thresholding approach was then applied to infer obscured or non-obscured conditions based on the mesonet's relative humidity, and these inferences were compared to the collected archived images of the target layer to evaluate the performance of the simple thresholding approach.

The scatterplots indicated that some, but not all, of the mesonet stations in both regions exhibited high RH levels when a ceiling was present at the mesonet elevation. The relationship however was more pronounced in the LA region, where 12 out of 22 station pairs had 75% of the mesonet observations ≥95% RH when a ceiling is present. In the GSM region, this behavior was observed in14 out of 56 station pairs, with the K1A5 ASOS representing half these pairs.

The assessment of camera imagery supports the potential for reliably detecting obscuration conditions at the mesonet, particularly when the relative humidity (RH) response at the mesonet approaches saturation in the presence of ceilings. Among the two thresholds attempted (95% RH and 98% RH), the 95% RH threshold performed better in detecting obscurations, with all probability of detection (POD) values above 0.9. In contrast, only 2 out of 7 station pairs had POD values above 0.8 for the 98% RH threshold. However, limitations in the archived camera imagery, such as the limited sample size at Clingmans Dome and lack of camera data for the study period in the LA region, highlight the need for further work to collect camera imagery, assess performance, and account for variability across different stations.

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