 |
 |
 |
 |
 |
 |
 |
 |
Activiities of ASTER Working Groups |
|
 |
|
 |
 |
|
 |
 |
The Institute of Psycial and Chemical Research)
Motoaki Kishino |
|
 |
|
Bodies of water such as the oceans and inland waterways and lakes have a significant impact on the environment. The major part of these water areas consists of water that has a high thermal capacity. The water areas are large thermal reservoirs if we consider the water areas as large water reservoirs. Therefore they have a significant effect on the climate.
The surrounding areas have a mild climate. They also dissolve various materials, hold them in suspension and transport them from the land to the sea. Plant plankton show an abnormal increase in lakes or enclosed bays close to populated areas due to this suspended matter or increased nutritients, resulting in effects on the environment for humans. On a global scale, once, the climate in Japan changes drastically when the El Nino phenomenon occurs, with a major influence on agriculture and fishing. More detailed observation and research are required in order to understand and solve these many problems.
Ships are generally used for the observation of areas of water. However, this has the disadvantage that data for the surrounding areas cannot be obtained, although detailed data can be collected at the observing point. On the other hand, since a satellite can periodically cover wider areas of water areas, we can observe an expansion of the phenomena that we could not obtain by using ships. A significant improvement is expected by combining ship observation and satellite observation. For these reasons, applied research projects in ocean and land water have been conducted in accordance with the development of ASTER.
We plan to apply the data from VNIR and TIR observations to the mapping of water surface temperature, water plants, turbidity, and other factors. |
|
 |
|
NOAA/AVHRR, a weather satellite with a ground resolution of 1.1 km, is the one that has been the most utilized of all TIR sensors ever operated. It could record the sea surface temperature very precisely by combining two thermal bands. Thanks to this, its data has been used for research on topics such as "front movement" caused by the collision of warm water and cold water and on "flush rising" pushed up from the deep sea. The ground resolution of ASTER TIR is 90 m, and it is expected to encourage detailed research on phenomena that NOAA/AVHRR was not able to deal with. This is the field of study mostly expected to make use of ASTER.
The temperatures recorded in thermal bands are lower than the actual values due to influences of absorbing materials such as water vapor in the atmosphere. Since the TIR absorption ratios of each band are different from each other, the water surface temperature can be obtained with a high degree of accuracy by combining several bands. In order to observe more detailed phenomena, it can, for example, be applied to expansion, mixing or dispersion at the mouth of a river or discharging outlets for waste water, to understand circulation flows or fronts in lakes or enclosed bays, or the distribution and movement of pollutants. |
|
 |
|
Plants in water or plants floating on the water surface are very productive, and they play a significant role in the substance circulatory system, not merely in the surrounding ecological system. For example, in lakes, plants wither, organic substances accumulate on the bottom layers, and bacteria propagate. Nutrient salts or gases are discharged into the air as a result of the activity of bacteria. These nutrient salts are utilized again by water plants and provide a habitat for fish. These relationships are complicated.
LANDSTAT or aircraft are utilized for research on the distribution of water plants, which is being carried out on lakes or coastal areas. ASTER has a plan to observe this distribution, utilizing the fact that the reflection rates from plant leaves floating on the water surface or from plant leaves above the water show lower in the red band and higher in the SWIR.
|
|
 |
|
Turbidity has been conventionally researched using VNIR sensors on LANDSAT or aircraft over lakes or coastal areas. In most of these cases, the turbidity has been assumed on basis of the relationship between the observation data from ships and satellites. However, in many cases the relationship will vary very greatly depending on the water area under observation or the time. Thus satellite data cannot be utilized without simultaneous observation data taken from a ship. The atmosphere also has a major influence on VNIR. It is one reason for different relationships at different locations or times. On the contrary, the atmosphere WG has been discussing atmospheric correction for ASTER, and it is expected to enable the collection of more precise data on turbidity.
Figure 1 shows images of the sea surface temperature and turbidity of Tokyo Bay on December 23, 1996. The images were obtained from LANDSAT/TM data based on ship observation. Since the data was obtained in winter, the sea surface temperature was 13 ℃ in the bay, and 16 - 17 ℃ in Sagami Bay. The Kuro Siwo [Black current] that is above 17 ℃ can be seen off the shore of Boso. A temperature front can be seen near the mouth of the bay. The turbidity is uniform within and outside of the bay. Very dirty seawater can be seen at the coastal areas.
Thus, various information on oceans such as the temperature distribution over a wide area can be obtained based on these detailed satellite images. It is possible to conduct researches on various physical phenomena in lakes or coastal areas such as the effect of river water flowing into the sea. In addition, the movement of warm waste water or pollutants can be understood, and then utilized for environmental monitoring of lakes or coastal areas.
At present, observations are being conducted on Mutsu Bay, Tokyo Bay, Ise Bay and Lake Shinji, aiming at establishment an algorithm for the distribution of the water surface temperature, water plants and turbidity by obtaining the relevant data. |
|
Figure 1
Sea surface temperature and turbidity in Tokyo Bay as observed by LANDSAT/TM (1996.12.23)
|
 |
Sea surface temperature
|
 |
| Turbidity |
|
|
( Eco/Oceanography and Limnology WG ) |
|
 |
|
