Research activity

Science is nothing but trained and organized common sense, differing from the latter only as a veteran may differ from a raw recruit; and its methods differ from those of common sense only as far as the guardsman's cut and thrust differ from the manner in which a savage wields his club.

T. H. Huxley ( aka "Darwin's Bulldog")

What Is Remote Sensing?

Remote sensing is a technique of acquiring, processing, analyzing and evaluating information on remote objects without making direct contact with the objects. The beginning of remote sensing goes back to the prehistoric time when life on earth was first created. In order to survive, living creatures had to identify distant objects and analyze whether the objects are friendly or enemies.
Human eyes, as an imaging device, do not have such a precision as high-resolution cameras; but combined with brain, they are an excellent "sensor" to identify the distance, position and physical characteristics of an object by detecting the light reflected from and radiated by the far-distant object. In remote sensing, "sensors" such as cameras and radars correspond to human eyes, and the techniques of computer processing, analyses and evaluation of acquired data act as a human brain.
The beginning of modern remote sensing began when photography was invented. Since then, the technique of photography utilizing the visible and infrared bands of EM (Electro-Magnetic) wave has advanced to an extraordinarily high-level. Currently, high-resolution cameras on board of aircrafts and satellites such as Landsat, Meteosat and Spot, are essential tools for earth observation. Optical sensors detect either the optical energy from the Sun which is reflected by objects, or the infrared heat radiated from objects. The obvious weakness of such "passive sensors" is that they cannot be utilized at their full extent under bad weather conditions and during nighttime.
Radars, on the other hand, are "active sensors" such that an antenna itself transmits illuminating microwave, and detects the energy of EM wave reflected and scattered by objects. Therefore, radars have day-and-night observation capability. Since, microwave, as compared with the optical waveband, has longer wavelengths ranging from 1 cm to 1 m, it penetrates cloud, mist and, to some degree, rain. Thus, radars operating at this microwave band have almost all-weather operational capability. While the microwave sensors having long penetration depth can provide information on the interior of vegetation and soil, which cannot be obtained by optical sensors, there exists a major problem that the analyses of such data become very difficult. At present, much effort toward overcoming this problem is being made in various countries in order to utilize effectively the large amount of potential information contained in the microwave data. Remote sensing has become an essential tool to understand the Earth environmental changes and their mechanisms, and to make appropriate action to improve the environment.
Synthetic Aperture Radar (SAR) is known as the "star" of microwave sensors. A spaceborne SAR at about 700~800 km above has an ability to distinguish objects separated by less than 10 m, and the spatial resolution of airborne SARs is becoming a sub-meter scale. These data are particularly useful over the areas where direct measurements on the ground and water are difficult to make, including desert, tropical rainforests, polar regions and oceans. Further, based on the interference phenomenon of EM wave, applications of InSAR (Interferometric SAR) can be made to making topographic maps, measurements of crustal movements by earthquake and volcanic activity, and mapping flow patterns of glaciers and ocean currents. In recent years, SAR polarimetry has gained considerable attention because of its potential information on the scattering processes. However, there still remain many unsolved problems on the techniques of relating quantitatively the acquired data to the physicalcharacteristics of the objects.

Research Fields

The aim of research in our laboratory is to contribute to the earth science and environmental problems using the SAR data acquired by satellites, aircrafts and Space Shuttles. The emphasis is placed on the basic research of the methodologies such as the optimal measurement techniques, sensors, improvement of the measurement accuracy, analysis and evaluation of remotely sensed data, and developing new methods and algorithms, analysis and evaluation of environmental information for better understanding of the planet Earth.
Because the acquired information is a result of interaction between the incident EM wave and objects, it is not possible to extract the physical characteristics of the objects quantitatively from the acquired and processed data without correct understanding the process of the mutual interaction. For this reason, basic researches have also been carried out to develop EM scattering theories, and to investigate experimentally the relation between the microwave scattered by water surfaces and soils and their physical properties.
The mottos of our laboratory are, "Ask yourself "Why ?"', "Check quantitatively", and "Search fundamental principle".


Research Subjects

Determination of Oceanic Phenomena by SAR (Synthetic Aperture Radar)

  1. Integration of ship detection algorithms by SAR with AIS (Automatic Identification System).
  2. Development of fundamental theories and applications of image analysis on oceanic internal waves, currents and bottom topography using SAR.
  3. Measurements of ocean currents by interferometric SAR and SAR complex data.
  4. Development of automatic target detection algorithms using split-look SAR data and non-Gaussian statistics.
  5. Effects of ships' pitching motion on SAR images.
  6. Determination of directional wave spectrum using split-look SAR data.
  7. Theoretical study on the relation between SAR images of ocean waves, velocity bunching and RCS modulations.
  8. Statistical analysis of azimuth streaks in the SAR images of breaking waves.
  9. Theoretical study and data analysis on the quantitative relation between the amount of wave breaking and K-distribution.
  10. Theoretical study and simulation of target detection on the sea surface using multipath sea echo.

Scattering of EM Waves
  1. Development of microwave scattering theories (Kirchhoff, composite models) from rough surfaces.
  2. Development of a basic theory and applications of probability density function of microwave RCS in terms of wavelengths of ocean waves.
  3. Measurements of penetration depth of X-band microwave into soil and dependencies of moisture content.

Applications of SAR/InSAR to Land Surfaces
  1. Estimation of the parameters of rice plants from satellite-borne (Radarsat) and airborne (AIRSAR, PI-SAR) SAR, InSAR and polarimetric SAR data.
  2. Development of the theory and applications on the retrieval of forest parameters from SIR-C/X-SAR multi-frequency/polarization Shuttle data obeying non-Gaussian statistics.
  3. Observation and analysis of the rainforests of Borneo, Malaysia using JERS-1 L-band SAR data.
  4. Statistical analysis of interferometric phase and change detection by InSAR.
  5. Dependence of auto- and cross-correlation functions of SAR images having non-Gaussian statistics on scattering media.

Statistical Analyses
  1. Developing empirical models for estimating forest biomass and deforestation using K-distributed amplitudes in the high-resolution polarimetric SAR images.
  2. Derivation of analytic solutions for non-linear speckle filters.
  3. Theories and applications on speckle noise reduction.
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