ISSN:0143-1161    

DOI:10.1080/01431168708948640

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Research results concerning tracers useful for estimating hydrodynamic surface flow are reported. Tracer characteristics analysed include spectral signatures, mapping transformations, sensor penetration depths, conservativeness and horizontal variability. Fluorescent dye is limited in usefulness to small area Lagrangean drift estimates. Suspended sediments and salinity are limited to single-date descriptive and Lagrangean drift estimates for estuarine and adjacent coastal waters. Chlorophyll pigments and surface temperature are the most ubiquitous properties and hold the most potential to be useful tracers. This is particularly the case for coarse- to meso-scale circulation of coastal ocean waters. Potential drawbacks of chlorophyll and surface temperatures as tracers must be overcome prior to their successful application for flow estimations by (1) compensating for non-conservative sources/sinks; (2) achieving imaging precision sufficient to resolve tracer levels at smaller space scale; and (3) acquiring the ability to remove spatially inhomogeneous atmospheric effects.

ISSN:0143-1161    

DOI:10.1080/01431168708948641

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Solar irradiance reflectance spectra of seawater with a variable content of particulate and dissolved materials as well as a variable bottom depth and composition were calculated. A two-flow radiative transfer model was employed, where the spectral signatures, characteristic for diverse seawater and bottom types, were introduced as input parameters. Optical signals in the spectral bands of LANDSAT MSS and TM, SPOT HRV and TIROS-N AVHRR scanners were computed in order to establish algorithms for remote determination of the bottom depth and composition. Several algorithms were proposed and their applicability discussed. The algorithms appear to be applicable down to depths of 3-20 m, depending on the water column and bottom composition.

ISSN:0143-1161    

DOI:10.1080/01431168708948642

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The traditional method for validating calculated values of chlorophyll concentration in the sea is based on comparisons within situpoint measurements made from ships. In this paper we present an alternative approach based on a two-look method involving data from successive orbits of the NIMBUS-7 satellite. We present the results of some calculations based on the use of Coastal Zone Colour Scanner (CZCS) data for the Irish Sea viewed from two successive orbits of the NIMBUS-7 satellite. The method used involves a first attempt at a self-consistent approach to calculating the aerosol path radiance. Results are presented for two pairs of scenes from 6 April 1980 and 4 May 1980.

ISSN:0143-1161    

DOI:10.1080/01431168708945372

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

In order to derive non-linear wave parameters from radar altimeter data it is necessary to model the return from the sea surface. Most models assume a Gaussian point target response for the radar, whereas in practice it was found for the SEASAT altimeter that the response was non-Gaussian. The effect of a non-Gaussian point target response on the retrieval of non-linear wave parameters is examined here, using a model based on a Gram-Charlier series. It is found that if the transmitted pulse width is sufficiently small then a non-Gaussian point target response has little effect on the retrieval of non-linear wave parameters.

ISSN:0143-1161    

DOI:10.1080/01431168708948643

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A technique is presented for measuring ocean wave directional spectra from aircraft using microwave Dopper radar. The technique involves backscattering coherent microwave radiation from a patch of sea surface which is small compared to dominant ocean wavelengths in the antenna look direction, and large compared to these lengths in the perpendicular (azimuthal) direction. The mean Doppler shift of the return signal measured over short time intervals is proportional to the mean sea surface velocity of the illuminated patch. Variable sea surface velocities induced by wave motion therefore produce time-varying Doppler shifts in the received signal. The large azimuthal dimension of the patch implies that these variations must be produced by surface waves travelling near the horizontal antenna look direction thus allowing determination of the direction of wave travel. Linear wave theory is used to convert the measured velocities into ocean wave spectral densities. Spectra measured simultaneously with this technique and two laser profilometers, and nearly simultaneously with a surface buoy, are presented. Applications and limitations of this airborne Doppler technique are discussed.

ISSN:0143-1161    

DOI:10.1080/01431168708948644

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

An increasingly common question arising in processing digital multi-channel data from spacecraft and aircraft scanner systems is “which channels contain the best information to separate the classes of interest to the user?”. This may be to identify the best single channel for separating classes in a black and white photographic or line printer output product, or the best three channels for a colour photographic presentation of the data, or the best ‘n’ channels to enter into a classification (being mindful of the ‘trade off’ between improved sub-class separability and increasing usage of computer space and time resources). The only valid way to approach separability using more than one channel is to consider it in multi-channel space utilizing the inter-channel relationship terms. Having defined the classes using some form of hierarchical ordering approach, such as that proposed by Andersonet al. (1972), the user may compile the statistical profiles of the classes of interest from the sensor multi-channel data. Based on these statistics a number of multi-channel separability indices may be derived. Each of these indices quantifies, on the basis of the user-defined multi-channel statistics, the degree of inter-class separability the user can expect as a function of subsets of channels drawn from the overall sensor channel set. This review considers some of the more common multi-channel indices of separability and presents the links between them. Their various properties, and some limitations, are also presented as is an operational approach to their use.

ISSN:0143-1161    

DOI:10.1080/01431168708948645

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A target calibration procedure for obtaining surface albedo from satellite data is presented. The methodology addresses two key issues, the calibration of remotely-sensed, discrete wavelength, digital data and the derivation of an albedo measurement (defined over the solar short wave spectrum) from spectrally limited observations. Twenty-seven LANDSAT observations, calibrated with urban targets (building roof-tops and parking lots), are used to derive spatial and seasonal patterns of surface reflectance and albedo for four land cover types, city, suburb, farm and forest.

ISSN:0143-1161    

DOI:10.1080/01431168708948646

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The Tethered Satellite System is a joint US-Italian programme for the study and design of a sub-satellite deployed from the Shuttle by means of a long tether. Two preliminary demonstration flights (the first upwards, the second downwards to 100 km) have been proposed to conduct several scientific and engineering experiments. Furthermore an improved multipurposes tethered platform is under study, to be deployed by future space stations at different low altitudes, where free-flying satellites have a short lifetime. Starting from the existing characteristics, the authors analyse the improvements necessary to achieve the performance required for remote sensing operational missions. Several authors have shown that, in station keeping, a tether control allows the longitudinal and in-plane/out-of-plane oscillations to be damped. Therefore the sub-satellite position can be accurately controlled and measured, also using active tracking systems during the short observation time interval. As far as attitude is concerned, a deeper study is needed to identify the attitude measurement and control systems of the future multipurpose platform. In order to obtain a design value representing the most stringent condition, the along-track stereoscopic coverage using linear arrays is considered. After an analysis of the attitude stability rate required by STEREOSAT and MAPSAT, and of the geometric errors involved in this kind of observation, it is shown that a value of 10−4deg/s or better will allow the multipurpose tethered platform to be used for different remote sensing missions.

ISSN:0143-1161    

DOI:10.1080/01431168708948647

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Spatial variations of the backscatter coefficient result from synthetic aperture radar imaging systems and their platforms. An adaptive algorithm has been developed to correct the multiplicative variation of the backscatter in the longitudinal (parallel to flight line) and lateral (perpendicular to flight line) directions. The coefficient of variation along the parallel and lateral profiles, which consist of the means of the pixels along these lines perpendicular to the respective profiles, is constant. This implies that the radiometric variations are multiplicative. Because standard correction methods such as polynomial transfer functions give unsatisfactory results, an adaptive correction algorithm was developed to correct these images. The algorithm produces a transfer function by means of a filtering window which moves along the profile in what is essentially a moving mean procedure. However, the length of the window is automatically adjusted as a function of the variation of the profile. The adjustment is based on a calculation of the probability that values to be included or excluded from the window belong to the included population. The effects of the successive correction steps were monitored using several thematic test sites. The resultant images provide both increased quality and quantity of data without any degradation of the statistical properties of the data.

ISSN:0143-1161    

DOI:10.1080/01431168708948648

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor