Remote sensing satellites for detecting glacier and ice sheet changes

Remote Sensing (satellite Images) and Climate Change

The objective of this work is to evaluate the role that remote sensing (satellite images) has played in studies of climate change. This work will focus on the terrestrial essential climate variables and place particular emphasis on how remote sensing is used as a tool for the detection of changes in ice-sheets and glaciers. Finally, this work will compare the use of satellite images with ground-based measurements in change direction of ice-sheets and glaciers.

It is reported by Vinnikov, et al. (1999) that in order to reveal "a long-term systematic climate trend, we need observations from a period long enough so that the influences of natural interannual and interdecadal climate variability, as well as random errors of observation do not create pseudotrends that are as large as the true climate trend." (Vinnikov, et al., 1999) Prior to satellite observations "sea ice records contained many regional gaps which lasted for months or for years." (Vinnikov, et al., 1999) These gaps have been filled by such as simple linear regression or climate averages and between sea ice changes in different ocean areas. However, none of these methods have proven effective in detecting long-term trends.

The work of Alley, Fahnestock, and Joughin (2008) entitled: "Understanding Glacier Flow in Changing Times" states that unexpected accelerations in outlet glaciers of the Greenland and Antarctic ice sheets in the last decade, in response to process not fully understood" resulted in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment to state conclusions that "poorly characterized uncertainties prevented a best estimate or upper bound on sea level rise." (2008)

It is reported that progress in Science in terms of understanding these environments which are very remote has progressed slowly "due to logistics, complex topography, paucity of field measurements, and limitations associated with information extraction form satellite imagery." (Alley, Fahnestock, and Joughin, 2008)

Stated as specific problems are the quality of information on:

(1) enumeration and distribution of glaciers;

(2) glacier mass-balance gradients and regional trends;

(3) estimates of the contribution of glacial meltwater to the observed rise in sea level; and (4) natural hazards and the imminent threat of landsliding, ice and moraine dams, and outburst flooding caused by rapid glacier fluctuations." (Alley, Fahnestock, and Joughin, 2008)

I. Essential Climate Variables

The work of Cawkwell (nd) identifies the 'Essential Climate Variables' as being those as follows:

(1) Atmospheric -- Air temperature, Precipitation, Air Pressure, Surface Radiation Budget, Wind Speed and Direction, Water Vapor, Cloud Properties, Carbon Dioxide, other greenhouse gases and aerosol properties.

(2) Oceanic -- Temperature, Salinity, Sea Level, Sea State, Sea Ice, Current Nutrients, Ocean Color, Co2 partial pressure, and Phytoplankton; and (3) Terrestrial -- River Discharge, Water Use, Ground Water, Lake Levels, Albedo, Land Cover, Fraction of absorbed photosynthetically active radiation (fAPAR) Local Area Index (LAI) and Biomass. (Cawkwell, nd)

II. Individual Levels of Assessments of Fluctuations of Glaciers and Ice Caps

Alley, Fahnestock, and Joughin (2008) state that a Global Hierarchical Observing Strategy (GHOST) was developed for the purpose of assessing the fluctuations of glaciers and ice caps. The individual levels of assessment include those as follows:

Tier I -- multi-component system observation across environmental gradients;

Tier II -- extensive glacier mass balance and flow studies in major climatic zones;

Tier III -- determination of regional glacier volume change within major mountain systems using cost-saving methodologies;

Tier IV -- long-term observation data of glacier-length change within major mountain ranges for assessing the representativity of mass balance and volume change measurements; and Tier V -- glacier inventories repeated at time intervals of a few decades by using satellite remote sensing. (Alley, Fahnestock, and Joughin, 2008)

III. Methods of Measurement

Alley, Fahnestock, and Joughin (2008) report that the comparison of multitemporal imagery is a method that is highly efficient for the purpose of measuring "terrain displacements." The work of De Angelis and Skvarca (2003) report that there is concern that the West Antarctic Ice Sheet will collapse due to ice shelf disintegration and that this concern is based on the indications that there would be a sudden and dramatic increase in the sea level. It is reported that the strongest evidence is derived from comparing "two high resolution optical satellite images" and specifically a Landsat 7 Enhanced Thematic Mapper plus (ETM+) image and an Advanced Spaceborn Thermal Emission and Reflection Radiometer (ASTER) image.

The work of Johannessen, Shalina, and Miles (1999) report the use of microwave satellite remote sensing data has been the basis of establishing a reduction of 3% every ten years in the "...areal extent of the Arctic sea ice cover since 1978." It is additionally reported that micro-wave derived sea ice time series are now among the longest continuous satellite-derived geophysical records. The Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) and the Special Sensor Microwave/Imagers (SSM/I) onboard Defense Meteorological Satellite Program (EMSP) satellite F8, F11, and F13 are stated to have made provision of data since 1987 and use a multifrequency brightness temperature data to make a calculation of total ice concentration and total ice extent. Calculated are: (1) total ice concentration; (2) area and (3) extent.

The following methods and instruments are used as well in monitoring global climate change:

(1) Scatterometry -- This is a microwave instrument used to measure the speed and direction of the wind over the oceans. The TRMM or Tropical Rainfall Measuring Mission is a method used to measure spatial and temporal variation of tropic rainfall and does so through use of a passive microwave sensor that is sensitive to liquid waters presence in the atmosphere. (Cawkwell, nd)

(2) GOME -- This instrument is used for scanning UV visible spectrometry in monitoring the global atmosphere.

(3) Cloudsat -- This is a cloud-profiling radar that uses low frequency to radar energy backscattered by clouds.

Summary and Conclusion

Remote sensing and satellite imagery has enabled scientists to carefully monitor the movements and changes in the earth's glaciers and ice shelves and this has been important since there are rapid changes occurring to the earth's surface. As noted in the work of Vinnikov, et al. (1999) before satellite observations were an option there were many regional gaps in the information on ice records and the methods previously used were not sufficient in mapping the earth's sea ice. However, satellite observations have enabled more accurate mapping of the earth's sea ice.

This study has identified the essential climate variables as being those related to the earths: (1) atmospheric data; (2) oceanic data; and (3) terrestrial data. Each of these categories is important in understanding the changes and movements of the earth's ice shelves.

This study has also noted that remote sensing and GIS technology play critical roles in the assessment of environments that are not only very remote but that are complex environments to analyze and model however, there are still many issues related to accurate mapping and assessment of glacier via satellite imagery technology. It is reported that the optimal method of accurate mapping and assessment is the combination of remote sensing and GIS technology in combination with field study.