Geodetic Imaging for Rapid Assessment of Earthquakes: Airborne Laser Scanning (ALS)
Abstract
To the residents of an area struck by a strong earthquake quantitative information on damage to the infrastructure, and its attendant impact on relief and recovery efforts, is urgent and of primary concern. To earth scientists a strong earthquake offers an opportunity to learn more about earthquake mechanisms, and to compare their models with the real world, in hopes of one day being able to accurately predict the precise locations, magnitudes, and times of large (and potentially disastrous) earthquakes. Airborne laser scanning (also referred to as airborne LiDAR or Airborne Laser Swath Mapping) is particularly well suited for rapid assessment of earthquakes, both for immediately estimating the damage to infrastructure and for providing information for the scientific study of earthquakes. ALS observations collected at low altitude (500—1000m) from a relatively slow (70—100m/sec) aircraft can provide dense (5—15 points/m2) sets of surface features (buildings, vegetation, ground), extending over hundreds of square kilometers with turn around times of several hours to a few days. The actual response time to any given event depends on several factors, including such bureaucratic issues as approval of funds, export license formalities, and clearance to fly over the area to be mapped, and operational factors such as the deployment of the aircraft and ground teams may also take a number of days for remote locations. Of course the need for immediate mapping of earthquake damage generally is not as urgent in remote regions with less infrastructure and few inhabitants. During August 16-19, 2010 the National Center for Airborne Laser Mapping (NCALM) mapped the area affected by the magnitude 7.2 El Mayor-Cucapah Earthquake (Northern Baja California Earthquake), which occurred on April 4, 2010, and was felt throughout southern California, Arizona, Nevada, and Baja California North, Mexico. From initial ground observations the fault rupture appeared to extend 75 km northwest, from the epicenter in Baja California through the US-Mexico border. The ALS observations were collected from an aircraft altitude of 600 m, flying at approximately 80 m/sec, using an Optech Inc. Gemini sensor, operating at 100 kHz, a scanning angle plus/minus 14 degrees and scan rate of 60 Hz. Some 24 lines, comprising a corridor 3 km wide and 106 km in length, were mapped, with a nominal point density of just over 10 points/m2. Total flight time for the project was just under 21 hours, but the laser on time was only 13 hours and 21 minutes. Preliminary versions of the observational data were delivered to the PIs (Michael Oskin, UC Davis, and Ramon Arrowsmith, ASU) within a few days of their collection. Geodetic imaging is still in its early stages of development, and ALS technology is progressing rapidly. The use of multiple channel (based on multiple lasers of the same or different colors and/or receivers operating in parallel) ALS units will result in contiguous sub-decimeter coverage, and deployment of ALS units in UAVs, with data transmitted to the operators in real time, will further reduce the turn-around time and enable more rapid assessment of earthquakes within the next decade.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.G11C..08C
- Keywords:
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- 1209 GEODESY AND GRAVITY / Tectonic deformation;
- 1225 GEODESY AND GRAVITY / Global change from geodesy;
- 1294 GEODESY AND GRAVITY / Instruments and techniques;
- 1640 GLOBAL CHANGE / Remote sensing