Velocity–Azimuth Display Analysis of Doppler Velocity for HIWRAP

Abstract

The velocity-azimuth display (VAD) analysis technique established for ground-based scanning radar is applied to the NASA High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP). The VAD technique provides a mean vertical profile of the horizontal winds for each complete conical scan of the HIWRAP radar. One advantage of this technique is that it has shown great value for data assimilation and for operational forecasts. Another advantage is that it is computationally inexpensive, which makes it suitable for real-time retrievals. The VAD analysis has been applied to the HIWRAP data collected during NASA's Genesis and Rapid Intensification Processes (GRIP) mission. The traditional dual-Doppler analysis for deriving wind fields in the nadir plane is also presented and is compared with the VAD analysis. The results show that the along-track winds from the VAD technique and dual-Doppler analysis agree in general. The VAD horizontal winds capture the mean vortex structure of two tropical cyclones, and they are in general agreement with winds from nearby dropsondes. Several assumptions are made for the VAD technique. These assumptions include a stationary platform for each HIWRAP scan and constant vertical velocity of the hydrometeors along each complete scan. As a result, the VAD technique can produce appreciable errors in regions of deep convection such as the eyewall, whereas in stratiform regions the retrieval errors are minimal. Despite these errors, the VAD technique can still adequately capture the larger-scale structure of the hurricane vortex given a sufficient number of flight passes over the storm.

An Automatic Recognition Method for Airflow Field Structures of Convective Systems Based on Single Doppler Radar Data

“…First of all, a velocity-azimuth display (VAD) algorithm [12] is employed to estimate the environmental wind velocities at different heights. Then, the estimated environmental winds are subtracted from the original radar velocity fields to eliminate their influence.…”

An LES-based airborne Doppler lidar simulator for investigation of wind profiling in inhomogeneous flow conditions

“…For airborne (or satellite-based) systems, the moving platform alters the measurement process and viewing geometry, thereby introducing new problems. These challenged have been investigated with statistical models (Baker et al, 1995;Gamache et al, 1995;Frehlich, 2001) or real measurement data (Leon and Vali, 1998;Weissmann et al, 2005;Tian et al, 2015;Chouza et al, 30 2016a). For airborne systems, Lorsolo et al (2013) and Guimond et al (2014) show the importance of model-based simulator studies, while relying on coarser resolution model output and focused on errors introduced due to the measurement system inaccuracies.…”

“…As of yet, a study analyzing the vertical wind through nadir or other measurement geometries such as Dual-Doppler have not been attempted for the medium-range aircraft. This study provides a critical component for an airborne Doppler lidar 10 system for boundary-layer research by investigating flexible scanning geometries theoretically, considering both wind profiling and nadir measurements of the wind field.Airborne Doppler systems are often used to assess wind profiles of the mean horizontal flow (Weissmann et al, 2005;De Wekker et al, 2012;Kavaya et al, 2014;Guimond et al, 2014;Tian et al, 2015;Baidar et al, 2018). The theory and problems associated with airborne Doppler wind profiling are very similar between lidar and radar systems.…”

“…Airborne Doppler systems are often used to assess wind profiles of the mean horizontal flow (Weissmann et al, 2005;De Wekker et al, 2012;Kavaya et al, 2014;Guimond et al, 2014;Tian et al, 2015;Baidar et al, 2018). The theory and problems associated with airborne Doppler wind profiling are very similar between lidar and radar systems.…”

“…In the ADLS two options for the separation of wind profiles (SEP) used for processing exist: 1. Retrieval of the wind profile in fixed, ground-based volumes with a given size that does not depend on the flight direction (Guimond et al, 2014;Tian et al, 2015). In this case, upwind flights contain more samples per given volume than downwind flights.…”