Automatic Detection and Classification of Orographic Precipitation using
Machine Learning
Abstract
Ground-clutter is a major cause of large detection and underestimation
errors in satellite-based (e.g. Global Precipitation Measurement Dual
Polarization Radar, GPM DPR) precipitation radar retrievals in complex
terrain. Here, an Artificial Intelligence (AI) framework consisting of
sequential precipitation detection and vertical structure prediction
algorithms is proposed to mitigate these errors using machine learning
techniques to uncover predictive associations among satellite- and
ground-based measurements aided by Numerical Weather Prediction model
analysis, specifically the High-Resolution Rapid Refresh (HRRR) model.
The framework is implemented and tested for quantitative estimation of
orographic precipitation in the Southern Appalachian Mountains (SAM).
Precipitation detection relies on a Random Forest Classifier to identify
rainfall based on GPM Microwave Imager (GMI) calibrated brightness
temperatures (Tbs) and HRRR mixing ratios in the lower troposphere
(~ 1.5 km above ground level). The vertical structure of
precipitation prediction algorithm is a Convolution Neural Network
trained to learn associations among GPM DPR Ku-band reflectivity
profiles, GMI Tbs, and orographic precipitation regimes in the SAM
including low level light rainfall, shallow rainfall with low-level
enhancement, stratiform rainfall with bright band, and deep heavy
rainfall with low- and mid-level enhancement. Vertical structure classes
corresponding to the distinct orographic precipitation regimes were
isolated through k-means clustering of ground-based
Multi-Radar/Multi-Sensor radar reflectivity profiles. The AI framework
is demonstrated for automatic retrieval of warm season precipitation in
the SAM over a 3-year period (2016-2019) achieving large reductions in
false alarms (77%) and missed detections (82%) relative to GPM Ku-PR
precipitation products, and significant rain-rate corrections (up to one
order of magnitude) by using a physically-based model to capture the
microphysics of low-level enhancement (i.e. seeder-feeder interactions).