Summer 2009 Research Experience for Undergraduates (REU) Program [website]
Automatic Ice Thickness Estimation from Polar Subsurface Radar Imagery
Mentor: Christopher Gifford

Abstract

This work focuses on automating the tedious task of estimating ice thickness from airborne radar data acquired over Greenland and Antarctica. This process involves the identification and accurate selection of the ice sheet's surface location and interface between the ice sheet and underlying bedrock for each measurement. Knowing the surface and bedrock locations in the radar imagery allows us to compute ice sheet thickness, which is very important for the study of ice sheets, their volume, and how they may contribute to climate change issues. The previous time-consuming manual approach required sparse hand-selection of surface and bedrock interfaces by several human experts, and interpolating between selections to save time. Two primary methods have been studied: edge-based, and active contour. Results are compared and presented in terms of time requirements, error, and advantages which each method offers. Automatic ice thickness estimation results from 2006 and 2007 Greenland field campaigns show that the edge-based approach offers faster processing (seconds compared to minutes), but suffers from a lack of continuity and smoothness aspects that active contours provide. The active contour approach is more accurate when compared to ground truth selections from human experts, and has proven to be more robust to image artifacts.

2008-2009 Undergraduate Research Team [website]
Defining The Antartic Ground Line
Mentor: Dr. Malcolm LeCompte

Abstract

Keywords:
Photoclinometry, Grounding Line, LANDSAT, Ice Sheet, GLAS
During the last century, ocean temperatures increased by approximately 1 Celsius degree. Long-term observations of portions of the coastal Antarctic ice sheet reveal increasing melt rates thought to be due to the ocean temperatures increase. As a result of the warming, ice sheet margins are observed to be retreating from the edge of the ocean by approximately 1 meter per year for each 0.1°C rise in ocean temperature. The area of the Antarctic ice sheet is thus in a state of flux.
As ice approaches the ocean from its landward, upslope side, it eventually enters the water and begins to float becoming an ice shelf. The relatively warm water at the base of the shelf causes it to melt into the ocean. The “Grounding Line” or GL is considered the point at which the grounded ice, in its continuous movement down-slope toward sea level elevation, enters the water and begins to float. It is more accurately referred to as the Grounding ‘Zone’ because the actual position fluctuates with tides and wave action.
It is difficult to determine the actual size of the Antarctic ice sheet due to the uncertainty in the location of the GL. Making an accurate determination of its location during a narrow temporal window (perhaps a 3-5 year interval) would be useful in estimating the mass-balance of the southern ice sheet simply by providing a perimeter across which the ice enters the water at a rate of 1 meter per year. This can be compared with the amount of precipitation observed to occur over the continental ice sheet.
Photoclinometry software obtained from NASA Goddard Space Flight Center was used to determine the geographic location of the GL. Photoclinometry uses differences in the surface brightness of LANDSAT scenes of coastal Antarctic, corrected for variations in solar illumination angle to determine relative slopes in a scene. The slopes were adjusted to actual elevations by associating brightness levels with actual elevations along scan paths of the GLAS (Geoscience Laser Altimetry System) laser altimeter GL
Terrain brightness was then compared between scan paths to produce an elevation map of a scene. The team derived an assigned portion of the Antarctic Ice Sheet GL along the coastline recorded by a LANDSAT scene centered at 120° West longitude.

Summer 2008 Undergraduate Research Experience (URE) Program [website]

Younger Dryas Impact Study
Mentor: Dr. Malcolm LeCompte

Abstract

The events precipitating the dramatic, millennial long climatic cooling known as the Younger Dryas, that occurred approximately 13,000 years ago remain a mystery. Recent evidence suggests an extraterrestrial impact on the Laurentide ice sheet may have provided the trigger for a massive influx of fresh glacial melt water theorized to have flooded the North Atlantic and shut down the Thermohaline circulation that moderates climate in the northern hemisphere.The apparent absence of an easily identified impact crater has focused the search for evidence of an impact on a search for extraterrestrial markers embedded in the Earth’s sedimentary record.

Association of an impact with coincident reduction in the numbers of megafauna species and human population of North America has suggested a strategy for the search for evidence of the impact. If an impact is responsible for initiating the onset of the Younger Dryas, the ultimate disappearance of megafauna species and the decline in human population, then the evidence should lie at the sedimentary boundary (YDB) separating the Younger Dryas from the preceding Bolling-Allerod at a depth corresponding to 12,900 years before present.

Some of these evidential markers (magnetic grains and spherules, charcoal, and glass-like carbon) was relatively easy to extract and identify while others (nanodiamonds and fullerenes) required great care, expensive instrumentation and considerable training. Fortunately, the vessels (carbon spherules) containing the more challenging markers were identified and extracted during the soil processing for magnetic spherules and charcoal. The research project also included an investigation of local paleo-lake depressions known to harbor impact markers and whose stratigraphy could have revealed a clearer understanding of the processes that shaped the coastal topography during the Younger Dryas. The research was carried out using a combination of Ground Penetrating RADAR (GPR) and sample coring to probe the subsurface deposits of selected depressions.

2007-2008 Undergraduate Research Team [website]
A Multiple Linear Regression of pCO2 against Sea Surface Temperature, Salinity, and Chlorophyll a at Station BATS and its Potential for Estimate pCO2 from Satellite Data.
Mentor: Dr. Jinchun Yuan

Abstract

A Multiple Linear Regression of pCO2 against Sea SurfaceTemperature, Salinity, and Chlorophyll a at Station BATS and its Potential for Estimate pCO2 from Satellite Data Abstract Ocean is one of the major reservoirs of carbon and can be a major sink of anthropogenic carbon dioxide. Together with pH, alkalinity, and total dissolved inorganic carbon (DIC), partial pressure of carbon dioxide (pCO2) is one of the four essential parameters for determining aquatic CO2 system. These four CO2 parameters are interrelated through chemical equilibrium and the determination of any two is sufficient for calculating the other two parameters. Ship-based oceanographic research cruise, that is expensive to operate and inefficient to provide global coverage, has long been the main source of data for characterizing oceanic CO2 system. Recently, Lohrenz and Cai (2006) conducted a field study of partial pressure of carbon dioxide, temperature, salinity, and Chlorophill a in surface waters of the Northern Gulf of Mexico and developed a correlation method for estimating carbon dioxide distribution from the Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing data. Although it showed great potential, the correlation is based on field data with a small temperature variation and atypical salinity for open ocean waters, and it is not clear whether it can be applied elsewhere in the ocean. Here, we proposed to extend the applicability of the method by conducting a data analysis study of field observations conducted at station BATS (Bermuda Atlantic Time-Series) Specifically, we have: (1) Obtain field data of alkalinity, DIC, temperature, salinity, and Chlorophill a determined at BATS station in the last two decades; (2) Calculate pCO2 from alkalinity and DIC; (3) Apply the correlation method to test the applicability of the method in the central Atlantic Ocean.