Wow there is a lot of Post-Sandy data out there! I was going through the latest list of geospatial and remotely sensed imagery products that is put together by the USDA, and realized this is quite an intimidating list for those folks that may not know what to do with all this data or how to apply it. Most folks want to know what the impacted areas looked like before and after the storm, and what data and tools are pertinent to them. So I thought I would take a few moments to pull together some more “user friendly” resources regarding post-storm imagery and lidar data. Please read to the end, because I have added in some cautionary statements on the use of some of this data.
Pre- vs. Post-Sandy Aerial Imagery
These viewers give you the ability to look at impacts of Sandy from the birds-eye view. This is especially helpful if you can’t physically get to these locations in a short amount of time.
Click and drag the white bar to compare historical and current imagery. You can also use the included bookmarks to explore some of the most damaged areas.
If you are unable to access your home, enter your address below and click locate. The map will zoom to the address entered and show any post-Sandy aerial imagery (from NOAA) available. You have to switch the basemap to imagery to see before and after. You can click on the green dots to see Civil Air Patrol Oblique Imagery as well.
This viewer provides access to all post-storm imagery from NOAA, and the data can be downloaded.
Enter an address or zoom in to get the flood data to show up. This site displays the different flood zones associated with Digital Flood Insurance Rate Maps. FEMA is working on Advisory Base Flood Elevations for the FEMA Region II coastal region in early December.
Using flood data of FEMA’s Hurricane Sandy Impact Analysis and the U.S. Geological Survey’s reports on high water marks, together with predictions based on the work of the U.S. Army Corps of Engineers, the WNYC’Data News Team has assembled a map that contrasts the two.
The FEMA GeoPortal has some great stuff. It was posted before, but there is new stuff up there now. I encourage you to take a look. Example map viewers include Sandy Impact Analysis, Housing info, Shelter info, Power info, Rental Resources, and a Coastal Flood Loss Atlas.
Post-Sandy Lidar Data
There are a lot of planes in the sky collecting data after a storm like Sandy. It is a wonder there aren’t more mid-air collisions! One of the datasets that is getting talked about a lot is post-Sandy lidar data. There are several agencies that are collecting lidar data post-Sandy. The USACE, USGS, and their contractors (PhotoScience and Woolpert) are all coordinating to make sure the areas impacted by Sandy are being captured by post-storm lidar. The area of coverage goes from Southern New England south to North Carolina, but only captures the open coast (beaches).
The Delaware Bay and Chesapeake Bay estuaries are not included. Also, this collection is just for a small swath of data right along the beaches, and in many cases does not cover the back bay/barrier regions. Each agency has slightly different reasons/authorities for collecting this data. Each also has different time frames for getting the data processed and delivered for public consumption. Most lidar data takes months to be collected and processed before it can be used reliably. Some of the near term products being developed and shown are based on preliminary data (not quality assured/groundtruthed).
The USGS uses this data to compare post-storm elevation data to lidar data collected prior to Sandy’s landfall to characterize the nature, magnitude, and spatial variability of hurricane-induced coastal changes, such as beach erosion, overwash deposition, and island breaching. They use a lidar sensor called the EAARL-B that can capture both topographic and bathymetric lidar. There are preliminary results, as well as other Sandy impact data posted on their Hurricane Sandy page at http://coastal.er.usgs.gov/hurricanes/sandy/.
The USACE uses this data to support regional sediment management, construction, operations, and regulatory functions in the coastal zone (for example, monitoring status of federal beach nourishment and storm damage reduction projects). They use a lidar sensor called CHARTS that can capture both topographic and bathymetric lidar.
<!– More info on USACE coastal mapping and the CHARTS sensor can be found at http://www.jalbtcx.org/Mapping.aspx –>
Topographic lidar captures the dry land elevation, and bathymetric lidar captures the submerged land elevation. Different laser wavelengths are used to capture data on land versus under water. The result is a smooth topo/bathy surface that can be used to define the entire beach profile where sediment transport occurs, and for modeling coastal inundation from storm surge and waves.
Comparing pre- and post-storm lidar elevation data enables you to see the immediate changes in elevation due to the storm. Things that pop out at you right away when looking at this data are the places where buildings have been damaged, where debris has collected, and where elevation of the beach (dune, berm, etc.) has changed. In many cases much of the sand that was on the beach is transported behind the dunes as overwash fans. Some great maps showing these types of changes can be seen here http://coastal.er.usgs.gov/hurricanes/sandy/lidar/.
Use with Caution
The temptation is to use the post-storm lidar for things like providing Advisory Base Flood Elevations (FEMA), redefining construction standards (V-Zones), and remapping beach setback lines (Coastal Programs). The problem is that this data is only a snapshot in time, right after the storm. Right away, states and municipalities are using bulldozers to scrape sand up into artificial berms to protect against the next storm. Sand is removed from the streets and put back on the beach. Waves and currents bring sand back onto the beach naturally. Beach renourishment projects take place to build up badly eroded areas for storm protection. A month or two after the storm, the post-storm lidar data is obsolete, and does not reflect the long term beach recovery. FEMA does not even use the post-storm lidar data to change their base flood elevations due to this reason. Long-term erosion rates are what are important for beach setback mapping, not episodic storms. Most coastal programs update setback lines on a 10 year cycle. Storms like Sandy get usually get “averaged” in.
The post-storm lidar can be used for more research endeavors, like determining how erosion control structures and renourishment projects fared. It can also be used for looking at scour at foundations or pilings and building design. These types of engineering analyses will use this data over time to provide recommended changes to construction standards, and for re-delineating erosion hazard zones. In the short term, this data should be used with caution.