Yasumasa Itakura

Statistical properties of the background noise for the atmospheric windows in the intermediate infrared region

Abstract The statistical properties of the sky-, forest- and cities-background noise for the four atmospheric windows in the intermediate infrared spectral region (2–14 μm) were analysed. There are the two kinds of spectral regions where the statistical properties about the amplitude distribution of the background radiance are quite different: one is the 2–3 μm region, being dominated by the scattering sunlight, the other is the 8–14 μm region, where the thermal radiation from the background is predominant. In the latter, the background noise is well described by the statistical model based on the random pulse process with the Gaussian amplitude and Poissons width distribution. In the former, both the amplitude and the width of the random pulse follow the Poissons statistics. The unified statistical model for the background noise including the whole intermediate infrared spectral region was derived. Its validity was confirmed with some experimental results.

Amplitude-modulated reticle constructed by a liquid crystal cell array.

A new type of amplitude-modulated (AM) reticle constructed by a liquid crystal (LC) cell array finds an excellent application in remote sensing for a flow velocity with unpredictable variation of speed and direction. The LC-AM reticle is a spatiotemporal spatial filter, optoelectrically achieved by using the consequent opaqueness due to the LCs dynamic scattering caused by the electric field sequentially applied to the respective LC cell. A feasibility test for the sensor with a pair of these reticles has measured the flow-velocity vector of a river.

Basic characteristics of ground vibration sensors for the detection of debris flow

Abstract An acoustic sensor has been designed and built to sense ground vibration with a microphone installed underground inside a steel pipe. The sensor has detected debris flows in torrents in Japan. Other sensors have been used to sense ground vibrations similarly and they also have been tested in the field individually. Basic characteristics of three different ground vibration sensors, an acoustic, a piezoelectric, and a moving-coil sensor are compared in the same test field. Two of them, a microphone sensor and a piezoelectric sensor, have higher signal-to-noise ratios (S/N ratios) than the moving-coil sensor. The microphone sensor has the maximum S/N ratio at our experimental field and is the most useful one.

Adaptive computer-based spatial-filtering method for more accurate estimation of the surface velocity of debris flow

An adaptive computer-based spatial-filtering velocimeter to measure the surface velocity of a natural debris flow with high accuracy is described that can adjust the filter parameters, specifically, the slit width of the filter, based on the surface-pattern characteristics of the flow. A computer simulation confirms the effectiveness of this technique. The surface velocity of a natural debris flow at the Mt. Yakedake Volcano, Japan, was estimated by this adaptive method, and the results were compared with those obtained by two other methods: hardware-based spatial filtering and normal computer-based spatial filtering.

Estimation of the surface velocity of debris flow with computer-based spatial filtering

A computer-based spatial-filtering velocimeter to measure the surface velocity of natural debris flow is described. This is a simple and interesting technique implemented with a spatial filter constructed as a software program that processes the video image of debris flow instead of a hardware implementation. The surface velocity of the debris flow at the Mt. Yakedake Volcano, Japan, was estimated by this computer-based spatial-filtering method, and the results were compared with those obtained by a hardware-based spatial-filtering method. Computer-based spatial filtering has the important advantage of a capability for tuning the spatial-filter parameters to the target flow.

Large motion estimation by gradient technique - application to debris flow velocity field

Abstract The gradient-based methods that are commonly used for the estimation of two-dimensional velocity field or optical flow behave poorly in the estimation of large motion. A preprocessing multiscale smoothing operation is proposed in the present paper to overcome this problem. Its effectiveness is confirmed by application to synthetic moving images and finally to the velocity field estimation of a natural debris flow along with a gradient-based method known as spatio temporal derivative space method.

Surface Velocity Computation of Debris Flows by Vector Field Measurements

Abstract The surface velocity of natural debris flows is one of the main physical parameters for developing effective disaster prevention techniques. The authors already presented the result of velocity vector field measurement of debris flow by the spatio temporal derivative space method. In this paper, we propose a multi resolution spatio temporal derivative space method, and apply the method to some real debris flow video images.

Debris flow velocity estimation: a comparison between gradient-based method and cross-correlation method

Debris flow causes lot of damages all over the world. The surface velocity of such a natural random flow is one of the important physical parameters that are considered in drawing a hazard map or constructing a sediment control dam. Gradient-based method along with a multiscale smoothing operation finds application in the two-dimensional velocity estimation of a debris flow from its video images. This paper investigates the performance of another optical flow determination technique - the cross-correlation method in the above application and compares the results with those obtained by the gradient-based method. A computer simulation with synthetic random moving images shows that the accuracy of the cross correlation method is higher than that of the gradient-based method.