Speckle noise appears in synthetic aperture radar (SAR) images as a random fluctuation in the images of random rough surfaces. Reduction of speckle noise is necessary for quantitative applications of synthetic aperture radar images to target detection and land cover classification. Multi-look SAR processing is usually used to reduce speckle noise at the expense of spatial resolution. This paper proposes a novel speckle reduction method in which multiple images processed by giving a velocity bias smaller than a resolution of velocity measurement device are added incoherently. Computer simulation results proved the validity of the proposed method.
In order to estimate the rate of particle elimination occurred on orbit, the fractions of eliminated particles from optical surfaces caused by centrifugal force or impact shock were measured. In the measurement of particle removing accompanying rotation, test particles were made to adhere to Si wafers and counted the number of particles by a laser microscope before and after rotation. Two types of rotational condition, fixed speed with various time of rotation and fixed time of rotation with various speeds, were adopted. As for the fixed speed of rotation, the fraction of remaining particles on a wafer had no significant correlation with rotation time. However, the fraction had a linear correlation with particle size. In the case of fixed time of rotation with different rotational speed, the fraction of remaining particles had linear relation with centrifugal force and the coefficient of first order depended on the particle size. On the other hand, impact shocks with various strengths were given to aluminum mirror using a free falling weight to evaluate the effect of impact shock on particle elimination. Particles more than 20, um were affected significantly by impact shock. Under certain strength of impact, the fraction of remaining particles was correlated with particle size by linear and the coefficient of the first order has the dependency on the impact acceleration. The impact direction also affected the fraction of remaining particles. Based on the measurements, the numerical computation was carried out to trace the change of a particle size distribution on optical surfaces probably occurred in orbit by an impact at satellite separation and mirror rotation. The initial condition of cleanliness level of a mirror was set as 15, 000particles/cm2 and percent area coverage of the mirror under the condition was 2.18%. The calculation showed that the percent area coverage would decrease to 1.33% just after the separation impact and reached 1.36% by the centrifugal force. The variation of the percent area coverage owing to the mirror rotation was not more than 0.18%. Accordingly, not only the particle elimination but also any other processes must be required in order to explain the increase trend up to 1.5% detected from interior lump calibration data of GLI.
Phenological eyes network (PEN) is designed as a validation campaign of satellite remote sensing data for terrestrial ecosystem observation. This project has started in several carbon-flux observatories of AsiaFlux projects. Main part of PEN consists of three core instruments : Automatic-capturing Digital Fisheye Camera (ADFC), HemiSpherical Spectro-Radiometer (HSSR) and SunPhotometer (SP). ADFC serves images mainly for a phenological study, sky condition and leaf area index (LAI). HSSR provides vegetation spectral parameters and a photosynthetically active radiation. SP provides atmospheric parameters for an atmospheric correction of satellite images. In combination with these PEN observations and flux or ecosystem research, validation study of ecosystem remote sensing will be enhanced in various aspects, namely, radiative quality check as well as ecological standpoints. PEN is an open project and welcomes involvements from various groups.