Hail Swaths Observed from Satellite Data and Their Relation to Radar and Surface-Based Observations: A Case Study from Iowa in 2009

Abstract

Several storms produced extensive hail damage over Iowa on 9 August 2009. The hail associated with these supercells was observed with radar data, reported by surface observers, and the resulting hail swaths were identified within satellite data. This study includes an initial assessment of cross validation of several radarderived products and surface observations with satellite data for this storm event. Satellite-derived vegetation index data appear to be a useful product for cross validation of surface-based reports and radar-derived products associated with severe hail damage events. Satellite imagery acquired after the storm event indicated that decreased vegetation index values corresponded to locations of surface reported damage. The areal extent of decreased vegetation index values also corresponded to the spatial extent of the storms as characterized by analysis of radar data. While additional analyses are required and encouraged, these initial results suggest that satellite data of vegetated land surfaces are useful for cross validation of surface and radarbased observations of hail swaths and associated severe weather.

Evaluation of approaches to identifying hail damage to crop vegetation using satellite imagery

“…Previous studies focused on identifying areas of damage by identifying NDVI change from a pre-event composite and post-event image (Parker et al 2005;Jedlovec et al 2006;Gallo et al 2012;Molthan et al 2013). In this study, an NDVI change product (threshold hereafter) is developed from the methods described by Molthan et al (2013) and Gallo et al (2012).…”

“…Gallo et al (2012) compared pre-and poststorm NDVI in the damage area to available radar data and ground reports of hail. NDVI imagery from before the event showed a uniform, green vegetation pattern across portions of central Iowa, with sporadic lower values representing urban areas.…”

“…Molthan et al (2013) examined hail swaths produced from severe thunderstorms that occurred on 18 August 2011 across extreme southeastern South Dakota, eastern Nebraska, southwestern Iowa, and northwestern Missouri. Molthan et al performed a similar analysis as Gallo et al (2012) but also incorporated observations with higher spatial resolutions from addi-tional earth-observing instruments, including Landsat-7 Enhanced Thematic Mapper Plus (30-m spatial resolution), Terra Advanced Spaceborne Thermal Emission and Radiometer (15 m), Système Pour l'Observation de la Terre-4 (SPOT-4, 20 m), and SPOT-5 (10 m). Molthan et al (2013) obtained similar results to those of Gallo et al (2012) with respect to the correlations between NDVI change and maximum estimated size of hail (MESH) size.…”

“…Molthan et al performed a similar analysis as Gallo et al (2012) but also incorporated observations with higher spatial resolutions from addi-tional earth-observing instruments, including Landsat-7 Enhanced Thematic Mapper Plus (30-m spatial resolution), Terra Advanced Spaceborne Thermal Emission and Radiometer (15 m), Système Pour l'Observation de la Terre-4 (SPOT-4, 20 m), and SPOT-5 (10 m). Molthan et al (2013) obtained similar results to those of Gallo et al (2012) with respect to the correlations between NDVI change and maximum estimated size of hail (MESH) size. Molthan et al (2013) used the higher spatial resolution sensors to confirm fieldscale damage and NDVI reductions in areas that corresponded to the MESH hail-fall streaks and coarserresolution MODIS observations.…”

“…Such an algorithm will assist in mapping hail damage following severe thunderstorms. The NDVI change threshold is based on the difference between a preevent NDVI composite and post-event single-day NDVI image, as used previously by Gallo et al (2012) and Molthan et al (2013). The anomaly detection technique uses single-day NDVI and LST anomalies to identify potential areas of damage.…”