A multiple scattering contribution is one of the major problems to be solved in the lidar measurements of clouds from space. This paper discusses the effects of the multiple scattering on the lidar signals measured from space and on the retrieval of the extinction profiles. A Monte Carlo model, which directly simulates the trace of photons in the clouds, has been developed for multiply scattered lidar signals. The probablity that the photon returns to the lidar receiver is calculated. By using the Monte Carlo model, numerical simulations have been made for space-borne lidar signals scattered from clouds. The results show that significant contributions of the multiple scattering in the lidar return signals lead to bias in the retrieval of the extinction coefficient of clouds. A technique to estimate the multiple scattering contribution in the return signal by using multiple field of view (MFOV) lidar has been developed by which the bias is considerably decreased.
For the purpose of establishing a vicarious calibration method to relate output digital numbers to surface radiance, an algorithm of reflectance-based method in the visible to near infrared region at the snow field was developed using a field measurement technique and radiative transfer code with the doubling-adding method. In this algorithm, most of the input parameters can be obtained from the field measurements, but some atmospheric parameters need to be calculated from the molecular and aerosol models. In this study, the vicarious calibration for Landsat Thematic Mapper was carried out at the Sarobetsu area in Hokkaido using the proposed algorithm. The calibration coefficients obtained from this vicarious calibration was nearly equal to ones.after 1987 which were reported in previous papers. This algorithm has enough potential as a vicarious calibration based on reflectance-based method with 5% error.
The four wave-length extinction coefficients for stratospheric aerosols observed with SAGEII (Stratospheric Aerosol and Gas Experiment II) were analyzed. SAGEII is an occultation sensor which have measured aerosol extinction at 1.02, 0.525, 0.453, 0.385, um from 10 km up to 45 km in altitude since 1985. The eleven years data record from 1985 through 1995 shows the strong increase in the extinction in 1991 after the eruption Pinatubo (June 1991, Philippine). The wavelength dependence of the extinction coefficients also significantly changed after the eruption, showing the existence of large particles. Even in the background period before the eruption, the wavelength dependence show significant spatial variation. The wavelength dependence would be good information to investigate micro-physical evolution processes of aerosol particles along with the transportation in the lower stratosphere.
The spectral properties of tree leaves throughout seasonal stages of ageing were measured using a spectrophotometer with an integrating sphere in the region of 350-2500nm. Changes occurring in the near-infrared region (760-910nm) were of most interest. Results were obtained first from spectral measurements of a single leaf, and then from multiple leaves. Spectral features of a single leaf with autumn senescence (yellow and red) showed significant change in the visible, and only slight change in the near-infrared. From the point of photosynthesis, vigor was lost in the autumn senescence leaf, hence, vigor of plants was not accessible with the reflectance of a single leaf in the near-infrared region. Leaf reflectance in the region increased as water was lost. This increase was due to leaf structure alteration as air voids increased inside. Spectral reflectance of a dead leaf in the near-infrared region showed "plateau rounding", whereas spectral reflectance of a live leaf in the near-infrared region showed "plateau". Total reflectance of multiple stacked autumn senescence leaves (almost pure yellow and pure red) in the near-infrared region was high due to high transmittance in the region. Total reflectance of multiple stacked dead leaves in the near-infrared region was low due to low transmittance in the region. The relation of spectral properties between visible and near-infrared regions demonstrated that VI and NDVI were a virtual index of the vigor of vegetation. In order to discriminate ecosystem types with terrestrial vegetation by the spectral changes of seasonal stages of ageing using remote sensing techniques, algorithms utilizing visible bands should be introduced.
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