Applications of Remote Sensing on the
Big Island of Hawaii

Lida Buster

Remote Sensing, Emporia State University

http://hvo.wr.usgs.gov/maunaloa/4303062_photocaption.html

Abstract

            The Big Island of Hawaii provides a unique environment for many applications of remote sensing. The island is comprised of five volcanoes, four of which are still considered active. Two of these volcanoes, Mauna Loa and Kilauea, are widely considered to be the most active volcanoes on Earth; Kilauea , in fact, has been erupting continuously since 1983. Due to the accessible nature of these largely effusive eruptions, the remote location of the island, and close proximity to a U.S. National Park, remote sensing research on the Big Island has become increasingly prevalent in recent years. This research has expanded knowledge of processes such as ground deformation associated with volcanism, climate change, and the weathering of surface basalts. 

Ground Deformation

            Until relatively recent years, scientists relied on field measurements to monitor the ground deformation associated with active volcanism. This usually involved EDM (Electronic Distance Measurements) and leveling surveys in the field using tiltmeters. The introduction of GPS (Global Positioning System) technology has significantly enhanced the capability to monitor volcanic ground deformation, as it offers several advantages over the traditional field techniques. As GPS monitoring has been shown to be more efficient, accurate, safe and convenient [than traditional methods], it is being increasingly used to analyze surface deformation.

            The Global Positioning System consists of an array of 24 satellites, each of which orbits the Earth at an altitude of approximately 20,000 km. The satellites complete two orbits daily, and transmit a continuous stream of information through radio frequencies. Each field GPS receiver has a view of between 5 and 8 satellites, depending on location. With combined data from these satellites, it is generally possible to calculate the position of each individual receiver to within a matter of meters. However, for the purpose of studying volcanic ground deformation, it is necessary to obtain accuracy within a matter of centimeters. This can be accomplished by emplacing several GPS receivers over a large number of benchmarks, allowing data to be concurrently collected. This large sample enables errors in observations to be systematically corrected.

            ADVANTAGES OF GPS

            1. No Line-of-sight required - Traditional survey techniques, such as EDM, required that a direct line-of-sight be established between benchmarks. This was usually difficult, both on steep stratovolcanoes such as Mount St. Helens and broad shield volcanoes such as Mauna Loa . Slopes of many volcanoes often obstruct the line-of-sight between benchmarks, prohibiting measurements from being made. Through the use of GPS, it is only necessary for benchmarks to have a clear line-of-sight to the sky, a task which is much more easily accomplished.

            2. Measurements can be made in almost any condition - In the past, weather was a major factor in determining when and where EDM and leveling surveys could take place. GPS allows near-continuous monitoring of ground deformation, regardless of most weather conditions.

            3. GPS Efficiency - GPS receivers are more portable and require fewer people to operate than traditional field measurement techniques. This a significant asset, as receivers are capable of operating continuously and unattended for periods of several months. Additionally, data can be transmitted in real-time and subsequently be more quickly analyzed.

Information for this section provided by the following URL:

http://volcanoes.usgs.gov/About/What/Monitor/Deformation/GPS.html

Image provided by:

http://volcanoes.usgs.gov/Imgs/Jpg/Monitoring/Deformation/32424296-29_large.jpg

Monitoring Atmospheric Conditions

          Studying the characteristics of aerosols in the atmosphere has become increasingly important in recent years. The distribution of atmospheric aerosols is relevant to many areas of interest, such as air pollution control, climate studies, and precipitation pattern research. Aerosols in the atmosphere directly influence the Earth's radiation budget, as they have been shown to produce a measurable cooling effect. Additionally, these aerosols can alter the properties of clouds, further pronouncing effects on the radiative balance of the planet.

            The Big Island of Hawaii offers a unique and advantageous location to study atmospheric characteristics, as it is situated in the middle of the Pacific Ocean , which acts as a buffer to reduce the effects of local anthropogenic pollution. Measurements taken here, therefore, more accurately reflect the mechanics of the atmosphere on a global scale. Over the last three decades, the Mauna Loa Observatory, or MLO, has operated a variety of lidar (Light Detection and Ranging) instruments to further investigate the properties of atmospheric aerosols. Lidar uses lasers to measure light which has been backscattered by particles and molecules present in the atmosphere. The lasers send out pulses of light which are then detected by a telescope. The Nd:YAG lidar, which MLO currently operates, emits these pulses at wavelengths of 532 and 1064 nm. The backscatter is then analyzed over multiple wavelengths, which allows total aerosol backscatter to be calculated as a function of altitude. Specific details on the MLO lidar are listed on the following chart.

Lidar Specifications

› Station Alt

3397m

› Latitude

19.539 N

› Longitude

155.578 W

› Time Zone

GMT -10

› Laser Type

Nd:YAG

› Frequency

Weekly

› Acq Board

MCS

› # Channels

4

› (nm) used

532, 1064

            It is interesting to note that there is an obvious correlation between total integrated aerosol backscatter and major volcanic eruptions. Well-defined peaks in total aerosol backscatter appear after the eruptions of El Chichon in Mexico , and Mt. Pinatubo in the Phillipines. The aerosols produced by these eruptions also reduced the total amount of solar radiation reaching the surface of the Earth. Pronounced dips in transmitted solar radiation are a direct result of the increased aerosol concentration following the eruptions.

Total Aerosol Backscatter

Information and images for this section provided by the following URL:

http://www.mlo.noaa.gov/programs/gmdlidar/mlo/gmdlidar_mlo.html

Determining Ages of Lava Flows

            Another application of remote sensing on the island of Hawaii involves the analysis spectral features of lava flows to determine relative age. Weathering of lava flows is characterized by defined mechanical and chemical changes. These changes produce distinct alterations in spectral reflectance curves, which can be then be analyzed to determine the relative ages of old lava flows.

            The visible and infrared spectrum of Hawaiian basalts is dominated by the presence of oxidized iron and vegetation. As the iron within the basalt oxidizes, the surface color most commonly changes from a black or dark brown color to a more reddish or tan hue. Additionally, as the basalt ages, it increases in reflectivity by approximately 6% (from an initial 5-7% to a final 12%). As this occurs, there is a simultaneous decrease in reflectance in the blue range of the visible spectrum, corresponding to the red colors associated with oxidation.

            Vegetation cover also increases as the flows age; this vegetation can be characterized, as the increase is systematic and well-defined. Vegetation coverage is more prominent on the east, or windward side of the island, which receives more rain. Here, it takes an average of 4,000 years for fresh basalt to become completely covered with full grown vegetation.

Information for this section provided by the following URL:

http://trs-new.jpl.nasa.gov/dspace/handle/2014/30898

Image provided by:

http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16705

REFERENCES

1. http://volcanoes.usgs.gov/About/What/Monitor/Deformation/GPS.html (accessed 11/28/07)

2. http://www.mlo.noaa.gov/programs/gmdlidar/mlo/gmdlidar_mlo.html (accessed 11/28/07)

3. http://trs-new.jpl.nasa.gov/dspace/handle/2014/30898 (accessed 11/28/07)

4. http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16705 (accessed 12/2/07)

5. http://hvo.wr.usgs.gov/maunaloa/4303062_photocaption.html (accessed 11/28/07)