Hongsuk H. Kim

Urban heat island

Abstract The phenomenon of an urban heat island was investigated by the use of Landsat/Thematic Mapper data sets collected over the metropolitan area of Washington, DC. By combining the derived spectral albedos and temperatures, surface energy composites of five surface categories were analysed. The results indicate that urban heating is attributable to a large excess in heat from the rapidly heating urban surfaces consisting of buildings, asphalt, bare-soil and short grasses. In summer, the symptoms of diurnal heating begin to appear by mid-morning and can be about 10°C warmer than nearby woodlands.

New Algae Mapping Technique by the Use of an Airborne Laser Fluorosensor

An airborne laser fluorosensor for the detection of algae in the sea has been developed. The system transmits dye laser radiation at 590 nm and monitors the fluorescent emission at 685 nm from chlorophyll-a a bearing microorganisms. The system was successfully flown over the test areas of Lake Ontario and Chesapeake Bay. The device is sensitive to a fraction of mg/M(3) chlorophyll-a density in the water from an altitude of 30 m.

Airborne bathymetric charting using pulsed blue-green lasers.

Laboratory and airborne experiments have proven the feasibility and demonstrated the techniques of an airborne pulsed laser system for rapidly mapping coastal water bathymetry. Water depths of 10 +/- 0.25 m were recorded in waters having an effective attenuation coefficient of 0.175 m(-1). A2-MW peak power Nd:YAG pulsed laser was flown at an altitude of 600 m. An advanced system, incorporating a mirror scanner, a high pulsed rate laser, and a good signal processor, could survey coastal zones at the rate of several square miles per hour.

Normalization of satellite imagery

Abstract Sets of Thematic Mapper (TM) imagery taken over the Washington DC metropolitan area during the months of November, March and May were converted into a form of ground reflectance imagery. This conversion was accomplished by adjusting the incident sunlight and view angles and by applying a pixel-by-pixel correction for atmospheric effects. Seasonal colour changes of the area can be better observed when such normalization is applied to space imagery taken in time series. In normalized imagery, the grey scale depicts variations in surface reflectance and tonal signature of multi-band colour imagery can be directly interpreted for quantitative information of the target.

Initial analysis of OSTA-1 ocean color experiment imagery

Ocean images were obtained at three widely separated locations on the earth as part of NASAs ocean color experiment. Digital computer enhancement and band-ratioing techniques were applied to radiometrically corrected spectral data to emphasize patterns of chlorophyll distribution and, in one case, of bottom topography. The chlorophyll pattern in the Yellow Sea between China and Korea was evident in a scene produced from shuttle orbit 24. The effects of the discharge from the Yangtze and other rivers were also observed. Two scenes from orbits 30 and 32 revealed the movement of patches of plankton in the Gulf of C�diz. Geometric corrections of these images permitted ocean current velocities in the vicinity to be deduced. The variability in water depth over the Grand Bahama Bank was estimated by using the blue-green channel of the instrument. The very clear water conditions in the area caused bottom-reflected sunlight to produce a sensor signal that was inversely related to the depth of the water.

A design study for an advanced ocean color scanner system

The spaceborne ocean color scanners currently being planned for flights on Nimbus-G satellite or space shuttle craft are, in every aspect, only a modest beginning towards what is to be expected of ocean color scanners in the eighties. Improvements are necessary in the following areas: present systems provide a spatial resolution on the order of 1 km at nadir, which would not satisfy most of the coastal zone study requirements. Also the present design of radiomers is less than optimum for the removal of the atmospheric effects on ocean colorimetry.Along with a colorimetric data analysis scheme, the instrumental parameters which need to be optimized in future systems are outlined. One technique for meeting these requirements entails use of large linear array detector technology.

Chlorophyll gradient map from high-altitude ocean-color-scanner data

A chlorophyll density map of an ocean area 25 x 30 km is presented, and the procedure used in generating the map from high-altitude ocean-color-scanner data is discussed. Data were obtained from a ten-channel radiometer on board a U-2 aircraft flying at 19.8 km above the coastal waters of Monterey Bay, California under conditions of clear skies and clear and deep water; the processing algorithms should be useful for satellite data as well. The total radiance measured at high altitude was separated into an atmospheric and sea-surface component and a water component, which is associated with chlorophyll content, for each pixel using the upwelling radiance of a near IR channel to estimate the atmospheric effect. Chlorophyll data were extracted by taking the ratio of the difference of intensities in the 472 and 506 nm channels to the sum of the channels, and are found to agree with shipboard chlorophyll determinations at a depth of 5 m.

Surface Radiation Budget Imagery

Linear regressions which summarize the relationships between the turbulent fluxes of heat and latent heat of vaporization leaving the surface and surface albedos are given. This observation is based on a semi-empirical analysis of the data collected from sets of Landsat/TM (Thematic Mapper) imagery as the top of the atmosphere images have been converted into maps of surface radiation budget. A preliminary analysis shows that in spite of the land surfaces temporal and spatial variability, the transfer of latent and sensible heat into the atmosphere would appear to be governed by the land surface albedo.

Sunlight Induced 685NM Fluorescence Imagery

The technique of remote sensing chlorophyll pigment concentrations by monitoring sunlight induced fluorescence at 685 nm is an alternative method of surveying the health and productivity of phytoplankton in the oceans . This method measures induced fluorescence from chlorophyll pigments whereas the conventional absorption method measures the reflectance ratio of blue/green channels as an indication of chlorophyll abundance in the water. It should be noted that the method is also differentiated from the laser induced fluorescence technique in which a laser is used to induce the fluorescence, whereas in this method a passive spectroradiometer or imager is used to monitor the occurrence of natural fluorescence under sunlight.

OSTA-1/Ocean Color Experiment

Ocean Color Experiment (OCE) on the OSTA-1 mission acquired ocean images at several widely separated locations on the earth. Digital computer enhancement and band ratioing techniques were used to emphasize patterns of chlorophyll and sediment distribution in the Yellow Sea and, in one case, of bottom topography in the Great Bahama Bank. Two scenes in the Gulf of Cadiz from orbits 30 and 32 were geometrically corrected to show the movement of plankton patches. This technique enabled ocean current velocities to be deduced. A duplicate of the OCE instrument mounted on a DFVLR aircraft was flown over an area of the Atlantic Ocean off the coast of Portugal during the Shuttle mission.