TOPIC 14

Environmental Monitoring & Assessment

Remote sensing is an important tool for environmental monitoring and assessment. Remote sensing can provide a record of change over time and can record this information for small and large areas ranging from a local to a global scale.

In addition to remote sensing images from satellites and aircraft, there are a variety of other sources of information which can be used for environmental monitoring and assessment these include:  topographic maps, digital terrain maps, land use and land cover maps and a variety of thematic maps.

Examples of environmental monitoring and assessment

Monitoring and Assessment of Natural Disasters

Affect of a hurricane on an area: Landsat Thematic Mapper satellite images taken before and after the hurricane can be processed in order to assess the damage on forest land.

Landsat TM prior to Hurricane Hugo 1981	Landsat TM after Hurricane Hugo 1983
	Changes in Forest Land After classifying the before and after Landsat TM images into thematic land cover consisting of Water, Forest, and Bare Soil, differences between the classified images are calculated to arrive at an assessment of change. Red depicts areas that were forested and are bare soil; Blue depicts water and wetlands; Green depicts forests not significantly affected by the hurricane.

Oil Spill detection and assessment: The areal extent of an oil spill can be tracked over time and the area impacted can be assessed.

The dark areas off the coast represent the areas where oil is present and areas of lighter tone directly south are areas where dispersant was sprayed on the oil to encourage emulsification. Oil, which floats on the top of water, suppresses the ocean's capillary waves, creating a surface smoother than the surrounding water. This smoother surface appears dark in the radar image. As the oil starts to emulsify and clean-up efforts begin to take effect, the capillary waves are not as effectively damped and the oil appears lighter. Size, location and dispersal of the oil spill can be determined using this type of imagery.

Oil Spill Wales coastline, England	Radarsat Image
	A supertanker, the Sea Empress, was grounded near the town of Milford Haven, Wales on February 15, 1996. After hitting rocks, the outer hull was breached and approximately 70,000 tonnes of light grade crude oil was dispersed southward under storm conditions.

Oil Spill - Coast of France	ERS Satellite (Radar)
	Monitored Parameters: Spill location Size and extent of the spill Direction and magnitude of oil movement Wind, current and wave information for predicting future oil movement

Ocean Color and Phytoplankton concentration

Ocean color analysis refers to a method of indicating the "health" of the ocean, by measuring oceanic biological activity by optical means .

Phytoplankton, are significant building blocks in the world's food chain and grow with the assistance of sunlight and the pigment chlorophyll. Chlorophyll, which absorbs red light (resulting in the ocean's blue-green colour) is considered a good indicator of the health of the ocean and its level of productivity.

Phytoplankton Concentration - NASA/NIMBUS CZCS Satellite
	Higher phytoplankton concentrations are displayed in green-yellow-red colors; lower concentrations in blue-magenta color. Note major discharge areas in low latitudes such as the Amazon River, South America have high phytoplankton concentrations along the coast due to discharges from rivers and nutrient upwelling.

The ability to map the spatial and temporal patterns of ocean color over regional and global scales has provided important insights into the fundamental properties and processes in the marine biosphere.

Phytoplankton Concentration - NASA/NIMBUS CZCS Satellite
	Higher phytoplankton concentrations are displayed in green-yellow-red colors; lower concentrations in blue-magenta color.

Mapping and understanding changes in ocean colour can assist in the management of fish stocks and other aquatic life, help define harvest quotas, monitor the water quality and allow for the identification of human and natural water pollution such as oil or algal blooms, which are dangerous to fish farms and other shell fish industries.

In general, ocean productivity appears highest in coastal areas due to their proximity to nutrient upwelling and circulation conditions that favour nutrient accummulation.

Mapping and monitoring ozone in the atmosphere

Ozone (O³) is produced in the upper atmosphere through the interaction of normal oxygen molecules (O²) with incoming ultraviolet radiation. It has the ability to prevent much of the ultraviolet radiation from reaching the surface of the earth, thus protecting animal life.

The Ozone concentration of the earth's atmosphere has been mapped by the NOAA/TIROS and NASA/NIMBUS satellite series since 1979. These studies are part of NASA's Mission to Planet Earth program which is part of the larger international Global Change Research Program.

In addition to ozone, the NIMBUS satellite also measured the amount of nitric acid in the upper atmosphere. These naturally occurring low levels of nitric acid in the atmosphere (up to12 parts per billion ) are produced by the interaction of nitrogen and oxygen in the upper atmosphere. In polar regions, atmospheric nitric acid is more concentrated reflecting the greater flux of charged particles and ultraviolet radiation.

Atmospheric Nitric Acid - NASA/NIMBUS satellite sensor
Left image is of the upper stratosphere; Right image is of the lower stratosphere;	Concentrations of atmospheric nitric acid: < 4 ppb = blue 4 to 12 ppb = green-yellow-red-white

Ozone in the atmosphere is destroyed by nitrogen-oxygen and chlorine-oxygen compounds - such as atmospheric nitric acid, so one would expect to see some ozone depletion in polar regions where there is an increase in nitric acid.Other compounds derived from aerosol sprays produce chlorine-oxygen compounds which also destroy ozone.

Other factors which may influence ozone levels and trace chemical levels in the atmosphere may be dependent on the changing geomagnetic field and influx of solar radiation.

Magnetosphere around the Earth (diagramatic view)

Variations in the Earth's Magnetic Intensity

Blue-Green denotes low magnetic intensity; Yellow-Red depicts high magnetic intensity.

Oceanic and Atmospheric Weather Phenomena

An important weather pattern which has become well known is the El Niņo phenomenon. The name El Niņo (The Child) refers to the warm ocean current that appears along the Pacific coast of South America each year around Christmas. For most of the year the easterly trade winds push warm equatorial surface waters towards Australia. This creates a surface divergence along the equator that is filled by cold, nutrient-rich water moving up from below (upwelling), forming a cold tongue in the eastern Pacific. This makes Peruvian waters one of the most productive fisheries in the world.

As the trade winds die seasonally, the bulge of water off eastern Australia flows back causing the warm water to float over the cold currents off Peru. This resulting increase in temperature which then temporarily causes the fish to disappear.

The El Niņo weather phenomenon is when this reversal in surface currents reaches extreme proportions and causes a change in traditional rainfall patterns and the release of large amounts of latent heat into the atmosphere. The subsequent energy propagates within the atmosphere, affecting the weather in various ways and places and disrupting the normal rhythm of life across the Pacific Ocean.

Satellite Remote Sensing of El Niņo phenomenon (1996-97)

Several different remote sensing satellites/sensors have been used to acquire regional/global information on ocean and weather phenomenon.

1) NOAA/TIROS satellite AVHRR sensor can measure the sea surface temperature using the thermal infrared portion of the spectrum. This provides information on the surface water temperature over the Pacific Ocean over time.

2) TOPEX/Poseidon Satellite/sensor measures the sea surface elevation which allows tracking of changes in sea level.

3) ADEOS (Advanced Earth Observing Satellite) with the NASA NSCAT wind sensor, which measures near surface winds over the ocean (both speed and direction).

4) NASA/NIMBUS satellite with the Coastal Zone Color Scanner (CZCS) measures the ocean color and the chlorophyll content (phytoplankton) which is an indication of the nutrient levels and bilogical health (and productivity) of the ocean.

The following animation is a representation of the environmental changes affecting the pacific ocean from data acquired by the first three remote sensing satellite systems: El Nino Animation

• During 1996, strong winds blowing from east to west pile up water in the western Pacific

• In the west, sea level and sea surface temperatures are higher than normal.

• In December 1996 and February 1997, two wind bursts blowing from west to east were observed.

• West winds generate 'Kelvin' waves (represented by sea level rise) which travels across the Pacific.

• Following the Kelvin waves, warming in the eastern Pacific, and cooling in the west are observed.

• Climatic effects of warm Pacific waters result in excessive rains which result in flooding and landslides in Central America and other anomalous temperature conditions in North America. Productive fisheries in Peru and western South American countries are significantly reduced. Normal commercial fish species replaced by exotic (tropical) fish species off California coast.

Biological effects of El Niņo using the NIMBUS CZCS Sensor (ocean color/health/phytoplankton)

Western North America: first four images are the expected average for each season; 1983 images show the lower concentration of phytoplankton than average due to El Niņo effect.

Western South America: first four images are the expected average for each season; In spring and summer 1982-3, pigments are drastically lower than usual and though they have increased by spring-summer of 1983-4 they are still reduced and restricted to a narrow region near the coast.

References:

Arnold:  p. 204 - 215

also:

Drury, S.A. (1990):A Guide to Remote Sensing, Interpreting Images of the Earth; Oxford University Press, 199 p.