ISSN:0143-1161    

DOI:10.1080/01431168608954703

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Remote-sensing techniques measure the radiance of the surface through a layer of atmosphere which both attenuates the signal and adds a path radiance. One class of solution can be found using the known dependence of transmittance on atmospheric path length. Multiheight measurements from aircraft enable the determination of transmittance and path radiance by linear regression. Multiangle measurements from overlapping aircraft scans have also been applied, but the difference of path lengths offered by the range of aircraft scan angles is insufficient to determine the atmospheric parameters with accuracy, especially with the uncertainties introduced by reflection from non-Lambertian surfaces.

ISSN:0143-1161    

DOI:10.1080/01431168608954704

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An analysis of the atmospheric radiative transfer processes suggests that the diffuse radiance emerging at the top of the Earth's atmosphere in the position of a satellite can be approximated by a linear relationship with the optical depth. It is found that the variation of the optical depth is associated with the changing of aerosol size distribution. The optical depth increases with the presence of large aerosol particles. Thus, inhomogeneities in aerosol size distribution can affect the high-altitude atmospheric radiance in the visible wavelengths (400–800 nm). To demonstrate an application of ocean colour remote sensing for atmospheric studies, computations of diffusely reflected radiance at the top of the atmosphere, using the radiative transfer equation, have been made for known aerosol size distribution and oceanic surface albedo. The condition of a clear sky over clear water has been considered in the study. The computed radiance was compared with the radiance detected by the Coastal Zone Colour Scanner (CZCS) aboard the NIMBUS-7 satellite. The CZCS radiance was collected within 1–2 hours after the aerosol measurements from the same area (Monterey Bay, California). An optical depth of the Earth's atmosphere is inferred from the comparison. The procedure was carried out for wavelengths corresponding to the CZCS channels (443, 520, 550,670 and 750 nm). Values of optical depth are plotted against the wavelengths to provide an optical depth spectrum. The results indicate that there is a strong dependence of optical depth on the wavelength. The dependence, however, does not agree well with the relationship proposed by Angstrom (1964) for the aerosol optical depth in the atmosphere. Furthermore, the resulting optical depth ratio cannot be estimated by the approximation suggested by Gordon and Clark (1981) and Gordon et al. (1983).

ISSN:0143-1161    

DOI:10.1080/01431168608954705

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Many measurements to satellites, whether of direct scientific interest or merely for tracking purposes, require a knowledge of the atmospheric propagation delay which affects the observation, The delay has to be precisely determined for such purposes as geodetic or navigation positioning using the TRANSIT system or GPS (Global Positioning system) and gravity-field determination by precise orbit determination using satellite laser ranging. In particular, the high accuracy of satellite altimetry can be severely degraded by propagation delays not only in the altimeter measurement itself but also in the tracking-system observations.

ISSN:0143-1161    

DOI:10.1080/01431168608954706

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Synthetic aperture radar (SAR) produces high-resolution images of the Earth's surface (and subsurface, under some conditions) by coherently processing the returns from a pulsed radar. It is an active sensor, hence is not dependent on natural illumination for its operation, and the comparative transparency of the atmosphere at centimetre wavelengths allows penetration of clouds and haze. SAR therefore offers considerable potential as an all-weather, all-time-of-day sensor, as long as propagation effects do not destroy signal coherence. A particularly useful way of viewing SAR performance is in terms of the synthetic antenna gain pattern, and performance measures derived from this pattern (e.g. spatial resolution, sidelobe energy). Perturbations of the phase due to irregularities in the refractive index structure of the ionosphere and troposphere lead to changes in the system performance. We have used a phase screen model to generate phase perturbations of the form expected due to propagation through a disturbed ionosphere. Simulations have been undertaken and used to assess the performance of a variety of SAR systems under particular geophysical conditions. These simulations indicate that at the longer wavelengths (C band and above), severe disturbances may greatly reduce image contrast, to the extent of destroying the image. Geometric distortions will also be introduced.

ISSN:0143-1161    

DOI:10.1080/01431168608954707

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The Utopian notion of position determination at sea is for an unlimited number of users to obtain an unambiguous, extremely accurate positioning facility, not only at the sea surface but also on the seabed or anywhere in between, 24 hours per day, continuously and in all weathers. This has traditionally implied such unattainable standards of technology that the notion has inspired little but cynical laughter. Now however, the notion has become reality for most of the practical situations encountered offshore. The question of how accurate a position should be can still evoke debate, of course, but only remote sensing and, perhaps, geodesy demand, on occasion, higher standards than are attainable by contemporary methods. This paper attempts to set in perspective the various methods employed to determine position offshore and to discuss in general terms the several approaches to the accuracy requirement.

ISSN:0143-1161    

DOI:10.1080/01431168608954708

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

This article describes a separability measure for class discrimination. This measure is based on the Fisher information measure for estimating the mixing proportion of two classes. The Fisher information measure not only provides a means to assess quantitatively the information content in the features for separating classes, but also gives the lower bound for the variance of any unbiased estimate of the mixing proportion based on observations of the features. Unlike most commonly used separability measures, this measure is not dependent on the form of the probability distribution of the features and does not imply a specific estimation procedure. This is important because the probability distribution function that describes the data for a given class does not have simple analytic forms, such as a Gaussian. Results of applying this measure to compare the information content provided by three LANDSAT-derived feature vectors for the purpose of separating small grains from other crops are presented.

ISSN:0143-1161    

DOI:10.1080/01431168608954709

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Cross-scan averages of forward and reverse scan are analysed to model the within-line sample-position-dependent noise of LANDSAT Thematic Mapper images, in cases where no radiometric saturation is present. Two sources of banding are discussed: the droop, already mentioned by other authors, and the so-called radiometric hysteresis. The defined models are used to generate a correction algorithm which has been tested with real data.

ISSN:0143-1161    

DOI:10.1080/01431168608954710

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Although the two largest rivers in China originate in the same region separated only by the Bayanhar Mountains as a watershed, the Yangtze and Yellow rivers behave in quite different ways. Most of the warm and humid air currents from the Arabian Sea and the Bay of Bengal are blocked by the Bayanhar Mountains. As a result the amount of water in the Yellow River is only 5 per cent of that in the Yangtze River. Based on the cloud coverage area and the cloud volumetric distributions, and also the thickness above 9-4 km of the cumulus clouds located north and south of the Bayanhar Mountains from the geosynchronous satellite infrared imagery, the results suggest that a more detailed investigation is warranted in the hope that the proper modification of cumuli north of the Bayanhar Mountains would enhance the rainfall over the fountainhead of the Yellow River.

ISSN:0143-1161    

DOI:10.1080/01431168608954711

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

In this paper an approach for the relative calibration of a SLAR image is discussed. By the use of a calibration curve, it has proved possible to transform raw radar image data into a relatively calibrated form. The results obtained by the use of such procedure show that various features on a radar image are separable across the whole swath.

ISSN:0143-1161    

DOI:10.1080/01431168608954712

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor