Takashi Ishiyama

Ground surface features of the Taklimakan Desert

Abstract In an attempt to utilize satellite data to obtain land surface features of Taklimakan Desert in China, in situ measurements of spectral reflectance of the land surface is made the portable spectro radiometer in the spectral range of 400 ∼ 2500 nm. The analyses of the data show following features. (1) The difference in spectral reflectance of different soils is comparatively small. (2) There is a tendency that spectral reflectance of soils increases with increases of wavelength, for example, the average reflectance of the sands in the periphery areas of Taklimakan Desert is 21 and 38% in visible and near infrared spectra respectively. (3) It is found that reflectance of the soils decreases with increase of moisture content. The large decrease is recognized in 1450 and 1950 nm spectra, water absorption bands. This fact suggests that the monitoring of soil moisture is possible by measuring the radiance at these spectra, thus Landsat TM Bands 5 and 7 will be effective for monitoring soil moisture content.

Relationship among vegetation variables and vegetation features of arid lands derived from satellite data

Abstract The correlation between vegetation index and physical parameters of vegetation was analyzed in order to monitor vegetation in an arid area based on satellite data. Results indicate that the vegetation index is highly correlated with physical parameters of vegetation, in particular, dry biomass and leaf area index (LAI). However the correlation coefficient between vegetation index and vegetation coverage is slightly low. Results of vegetation monitoring based on satellite data which are analyzed by an algorithm we developed can be utilized to study desertification and the vegetation environment.

Extraction of vegetation cover in an arid area based on satellite data

Abstract An attempt is made to derive a vegetation index applicable for extraction of vegetation cover in an extremely arid area such as Taklimakan Desert from Landsat TM image data. In this method a ratio of vegetation coverage in each pixel is computed from the ratio of Landsat TM band 5 and 7 digital values. Then if the value of the ratio is larger than the threshold NDVI (Normalized Vegetation Index, Rouse et. al., 1974) is selected while if the value is less than the threshold SAVI is selected thus the vegetation index consisting of combination of NDVI and SAVI is made which can be defined as NDSAVI. The threshold is decided as follows. The reflectance in the spectral bands corresponding to TM band 5 and 7 is measured for various places in Taklimakan Desert using spectral radiometer which are compared with NDVI and SAVI and an appropriate threshold is decided. It has been confirmed that NDSAVI map shows better correspondence with actual vegetation cover in an arid area than single NDVI or SAVI maps.

Modeling of a photosynthetic crop production index for early warning using NDVI and meteorological data

This paper aims to develop a remote sensing method of monitoring grain production in the early stages of crop growth. It is important to oversee the quantity of grain in production at an early stage in order to raise the alarm well in advance if a poor harvest is looming, especially in view of the rapid population increase in Asia and the long-term squeeze on water resources. Grain production monitoring would allow orderly crisis management to maintain food security in Japan, which is far from producing enough grain for its own population. We propose a photosynthesis-based crop production index CPI that takes into account all of: solar radiation, effective air temperature, vegetation biomass, the effect of temperature on photosynthesis by leaves of grain plants, low-temperature sterility, and high-temperature injury. These later factors, which extend the model of Rasmussen, are significant around the heading period of crops. The proposed photosynthesis-based crop production index CPI has accurately predicted the rice yield expressed by the Japanese Crop Situation Index in three years, including the worst yield in recent years, at a test site in Japan.

Influence of look-angle on the water surface temperature observed with an IR radiometer

Abstract The analysis of the data of sea surface temperature observed with a portable infrared radiometer from the fixed point on the seashore indicates a significant effect of observation(look) angle when it becomes larger than 70 degrees. An attempt is made to explain the effect by applying Fresnels reflection law. A verification indicates a good agreement between the sea surface temperature observed with a portable thermal IR radiometer at large observation angles and that computed from Fresnels reflection equation.

Photosynthetic rice production index for early warning using Remote Sensing and meteorological data

This research aims to develop a remote sensing method for monitoring grain production in the early stages of crop growth in Japan and Asia. A photosynthesis based crop production index CPI for rice is proposed that takes into consideration the solar radiation, the effective air temperature, and NDVI as a factor representing vegetation biomass. The CPI index incorporates temperature influences such as the effect of temperature on photosynthesis by grain plant leaves, low-temperature effects of sterility, cool summer damage due to delayed growth, and high-temperature injury. These latter factors are significant at around the heading period of crops. The CPI index for rice was validated at ten monitoring sites in the central and northern half of Japan. The method is based on routine observation data, allowing automated monitoring of crop production at arbitrary sites without any special observations. The CPI index is applied to rice production in five regions of China, using solar irradiation data from the Japanese Geostationary Satellite, the Normalized Vegetation Index (NDVI) derived from NOAA AVHRR, and world weather data.

Development of BRF (Bidirectional Reflectance Factor) facility and its preliminary results

Abstract A portable apparatus developed by one of the authors to measure the Bidirectional Reflectance Factor (BRF) over the spectral range 300–1100nm is described. Preliminary results of BRF for vegetation of different height and bare land indicate an effect of view direction on BRF. The analysis of the observed data also indicates that the larger the vegetation size the larger the dependence of reflectivity on viewing direction.