My overall research interests lie in the improved understanding of Earth dynamics including earthquakes, volcanism, lithosphere process, plate tectonics, cryosphere mass balance, sea level change, and hydrology, by applying a variety of traditional or remote sensing measurements to answer open science questions.
Measuring volcano eruption using satellite imagery (2016-2017)
Measuring lava flows from satellite photogrammetry (published in GRL, 2017). The figure below shows the lava flow field (overlapping red map) resulting from the 2012-13 eruption of Tolbachik volcano in Kamchatka, Russia, measured from ArcticDEM digital elevation models. The background is the hillshade of the high resolution topography created by the Polar Geospatial Center from DigitalGlobe, Inc. imagery.
Measuring river heights using satellite imagery (2016-2017)
We develop a new methodology by using ArcticDEM data for measuring river water surface elevations without the need for in situ data (published in GRL, 2018). River surface heights are estimated by precise detection of river shorelines and mapping of shorelines to land surface elevation. The animation shows the detection of river shorelines change along a reach of Tanana River near Fairbanks, Alaska. As shown, the river width gradually expands due to seasonal variations. Imagery ©2011-2014 DigitalGlobe, Inc.
Earthquake modeling using satellite gravimetry (2012-2015)
Undersea earthquake is one of the most devastating natural hazards facing mankind. Earthquakes can cause Earth’s mass redistribution; hence permanently change the Earth’s gravity field, which has been monitored by the satellite mission — the Gravity Recovery And Climate Experiment (GRACE). We conducted source models inversion for several undersea earthquakes using GRACE-observed gravity and gravity gradient change measurements. The targeted earthquakes include the 2004 Sumatra-Andaman earthquake, the 2010 Maule, Chile earthquake, the 2011 Tohoku earthquake, the 2012 Indian Ocean earthquakes, the 2007 Bengkulu earthquake.
Our study reveal that the gravity data from the satellite mission — the Gravity Recovery and Climate Experiment (GRACE) — actually has a particular component (north component) that contains higher frequency coseismic signals compared to the other commonly used component of gravity (down component). This finding has been published in Geophysical Research Letters in 2014 and Earth and Planetary Science Letters in 2016, showing the improved seismic signal retrieval by using the north component of the GRACE gravity change for several undersea earthquakes.
Question 1: From the same measurements, how can one form of quantity (north component of gravity) contain more signal than the other quantity (down component)?
Answer 1: The explanation is somewhat similar to the case with GPS data processing, where the double-differenced measurements can reduce systematic errors and improve the positioning precision compared to single receiver measurements. Here, the north component of gravity through differentiation of the disturbing potential along the meridian direction can reduce the north-south ‘stripes’ noise in GRACE; hence reduce the noise level and reveal more high frequency coseismic signals.
Dai, C., C. Shum, J. Guo, K. Shang, B. Tapley, R. Wang, Improved source parameter constraints for five undersea earthquakes from north component of GRACE gravity and gravity gradient change measurements, Earth Planet. Sci. Lett., 443, 118-128, 2016.
Dai, C., C. Shum, R. Wang, L. Wang, J. Guo, K. Shang, and B. Tapley, Improved Constraints on Seismic Source Parameters of the 2011 Tohoku Earthquake from GRACE Gravity and Gravity Gradient Changes, Geophys. Res. Lett., 41, doi:10.1002/2013GL059178, 2014.
The following animations demonstrate the sensitivity of satellite gravity data to fault parameters:
Strike angle
Rake angle