September 21, 2021 Meeting

The first meeting of the 2021-2022 year was held virtually via Google Meet. Our guest speaker was Daniel Lamb from NWS Jackson MS.

Meeting Minutes

Call to Order
The first meeting of the 2021-2022 AMS/NWA chapter occurred on September 21, 2021 virtually via Google Meet. The meeting was called to order at 7:02pm by President Thomas Winesett.

Rolls
Recording Secretary Joanne Culin took note of the number present. In total, there were 14 present.

Minutes Approval
Given the virtual format of the meeting, we did not cover minutes from the previous meeting.

New Business
Eric sent a google form for officer nominations and he will check the results in a few days.

Treasurer David Cox gave the treasury report, which we have $452.29. Since we continue to do virtual meetings we are not collecting dues at this time, as we are not incurring travel expenses for speakers or food for meetings.

Our guest speaker for the evening was National Weather Service meteorologist Daniel Lamb. Daniel spoke about a technique that he has worked with to help improve information used for storm surveys. He gave a basic review of how the NWS performs damage assessments. Surveys are conducted to assess storm damage following severe thunderstorms and tornadoes. Advancements in technology have helped streamline the surveying process. This includes the development of the Damage Assessment Toolkit and the utilization of tornadic debris signatures. However, even with these advancements there remain challenges in conducting ground surveys. These challenges include insufficient road networks and closed roads due to flooding or other barriers. While satellite imagery has been used in the past for filling in survey information, this method that Daniel presented on is a different approach to utilized satellite data.

The data that is used in this presentation is from the Sentinel-2 satellite, which is operated by the European Space Agency. The advantage of using this data is that it is easy and quick to access. While it may not locate individual downed trees, it is useful for swath information. You can access this information via the Sentinel-Hub website(https://www.sentinel-hub.com/about). The website has a way to view different days and the period of record goes back a while. You can download images and use GIS software to view this and tinker with the imagery.

The images Daniel used were composites of true color and NDVI(normalized difference vegetation index which highlights areas of green vegetation, which is helpful in finding that versus dead vegetation in damage swaths). By using GIS software, he created difference images of the track area before the tornado and after the tornado.

Daniel then showed several examples of using this technique in April 2020. The first was for an Avoyelles-Catahoula-Concordia parish tornado. The storm had a history of producing tornadoes and there was a TDS on radar. This survey was challenging because it straddled between two county warning areas, and roads were closed across a stretch of land in a wildlife refuge. In addition, other roads were closed due to flooding. The assumption was that this was a continuous track until satellite data was utilized. It was then noted, looking at difference images, that there were two distinct tracks, which aligned well with how a tornado might track. Adjustments were then made to the track information.

Daniel showed another example of a tornado that went through the Delta National Forest. It had a well defined debris signature but it occurred over a sparsely populated area, and did not cross any general public roadways. In addition, parts of the area were flooded from the backwater of the Yazoo/Mississippi Rivers. No damage was found to have occurred along the roadways and aerial imagery was the only timely approach since the backwater flooding would persist for quite a while. The satellite imagery was eyeballed to determine a rough path length, but with little confidence and it was rated conservatively based on known EF scale tree damage indicators. Difference images refined the path length even more.

The final example that was used was the Marion County tornado that took place during the Easter event in 2020. There was clear damage and this was confirmed extensively by ground surveys. One primary area that was difficult to survey was in the Pearl River bottom. There was high confidence that this was a continuous path but the Sentinel data and image differencing technique helped fill in the gaps and provide further path width information.

Daniel also spoke about the limitations of using aerial imagery in doing damage surveys. For instance, the ability to rate tornadoes is limited. Most damage indicators that are used to rate tornadoes need to be accurately assessed using ground surveys. Satellite imagery is mainly limited to assessment of tree damage. Tree degree of damage is currently based more on type of tree damage than the extent of damage(which is what aerial imagery would provide). Not all tornadoes are apparent using Sentinel data/image differencing, especially in areas where there is limited tree cover. Damage paths are more likely to be seen in the EF1/EF2 range and higher. Overall, this type of technique is just another tool to use when conducting damage assessments. It does not provide enough information on its own but is another tool to use to complete the whole picture of a tornado event and provide better information for the historical record.

Adjournment
The meeting concluded around 7:54pm.

Minutes were submitted by Joanne Culin, Recording Secretary.