ISSN:0143-1161    

DOI:10.1080/014311697218025

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/014311697218034

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Erta 'Ale volcano, sited within the Afar Triangle of Ethiopia, is one of the least frequented, perennially active, subaerial volcanoes. By compiling a time series of Landsat MSS and TM, JERS-1, SPOT, and AVHRR digital imagery, and space-borne photographic data, we have been able to constrain the activity of this volcano, important for its geodynamic setting, during the long period since 1974 when volcanological investigations effectively ceased. Existing techniques for infrared thermometry have been modified to cope with saturation of the short wavelength infrared Landsat TM band 5 and 7 sensors, enabling derivation of thermal fluxes from Erta 'Ale's active lava lakes. Lake levels have been estimated from measurements of shadow lengths cast by the crater rim. Changes in caldera and flank reflectances identify new lava flows whose areas and volumes we have constrained in order to derive eruption magnitudes and effusion rates. Between 1968 and 1974, approximately 3 1010 kg of lava was erupted at peak discharge rates exceeding 400kg s -1, though much of this subsequently drained back or subsided rigidly. No post-1974 overflows were detected in the imagery, although thermal (100-400 MW) output from the lava lakes, and gas emissions appear to have been sustained up to the time of writing. The longevity of the lava lakes provides evidence for convective circulation between the lakes and a deeper magma reservoir. The high heat flux and low exogenous growth rates ( 10kg s -1 integrated over the last thirty years) are indicative of a volcano that 'grows' largely by magmatic intrusion, which is consistent with the formation of new igneous crust in the extensional tectonic environment of northern Afar.

ISSN:0143-1161    

DOI:10.1080/014311697218043

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A new approach has been introduced to measure statistically haze as generated by dust particles in the atmosphere in an arid area. By using Landsat-5 Thematic Mapper data in an optical waveband, it has been demonstrated that spatial disaggregation of the area under study is logically desirable and practically feasible. The approach essentially requires a reference data set acquired in hazefree conditions. The output is restricted to only the overall haze estimates.

ISSN:0143-1161    

DOI:10.1080/014311697218052

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We present the results of hybrid unsupervised-supervised classification of a series of Landsat-MSS images, spanning the period from 1978 to 1992, to study the impact of SO2 emissions from the nickel smelter at Monchegorsk (67 55 N, 32 50 E) in the Kola Peninsula, Russia, on adjacent boreal forest and upland (lichen-dominated) tundra vegetation. Ground truth data were collected from a 2500 km2 area during airborne and surface field campaigns in 1994 and 1995, and used to classify the 1992 image into 56 different surface types, including a characterisation of the level of vegetation damage. The pre-1992 images could not be classified by transferring the spectral signatures from the 1992 image, mainly as a result of phenological differences. Instead, they were classified using spatial context and a set of observationally-derived botanical rules governing the types of allowable land-cover change. A comparison of the classified images was performed by further combining the land-cover classes into groups representing forest areas with varying proportions of canopy damage, and upland tundra areas with varying degrees of lichen cover and damage level. Quantitative comparative results were obtained for a 22 225km2 area common to all images after 1978. Although damage levels were already significant by 1980, our results show that most of the increase in vegetation damage since 1980 has in fact occurred since 1989. We attribute this to a change in the local meteorological conditions. The method developed in this paper has the merit of revealing areas of upland tundra vegetation showing early effects of SO2-induced damage. It should thus have widespread applicability to the delineation and monitoring of areas of industrially affected arctic vegetation, especially in the former Soviet Union, where many such areas occur, often in regions where access is severely limited. However, it is likely that field validation will continue to be required, since the mechanism by which increasing damage levels are depicted in MSS images of lichen tundra areas remains unclear.

ISSN:0143-1161    

DOI:10.1080/014311697218061

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Many algorithms have been developed to retrieve precipitation and cloud liquid water from passive microwave measurement at mid-latitudes and in the tropics, but these algorithms do not necessarily work well over the ice-free oceans that surround the Antarctic continent where most precipitation falls in the form of snow.It is known that the clouds that produce most of the precipitation over the southern latitudes are thin stratiform clouds and the precipitation they give is of slight intensity (less than 0.5mm h -1 rain equivalent). In this paper the polarization corrected temperature (PCT) method for detecting precipitation is applied and compared with a new physical method that simultaneously retrieves both cloud liquid water and precipitation amount. Both methods are compared with the few in situ measurements available. The new iterative physical method is found to give better results and does not need any empirically derived parameters.

ISSN:0143-1161    

DOI:10.1080/014311697218070

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper we have developed some improvements on the commonly used methodologies in order to obtain accurate maps of sea surface temperature (SST). These improvements permit us: (1) to calibrate without bias AVHRR channels including non-linear corrections; (2) to get geometrically corrected maps for the complete scan width of AVHRR (3000 km) with a subpixel accuracy; (3) to detect clouds over the sea; and (4) to make atmospheric and emissivity correction for all zenith angles from nadir to the outermost off-nadir view of AVHRR images (68.9 ) and for different types of atmospheres. The theoretical base of the improvements used is detailed in each section, and an example is also included in each section in order to better explain how they are applied in a practical situation. The methodologies developed here can be profitable for any user interested in accurate retrievals of SST such as meteorologists, climatologists and oceanographers.

ISSN:0143-1161    

DOI:10.1080/014311697218089

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper we have developed some improvements in order to obtain accurate Sea Surface Temperature (SST) maps with APT (Automatic Picture Transmission) data transmitted in real time from NOAA satellites. The methodology proposed can be profitable for any user interested in accurate retrievals of SST such as meteorologists, climatologists and oceanographers. APT data are converted to 10-bit digital data like in HRPT images in order to perform calibration. Geometric correction is achieved with a subpixel accuracy for APT images. Small clouds are avoided by means of the technique of universal kriging. A single-channel method using radiosounding data has been developed for the atmospheric and emissivity corrections. Atmosphere has been radiometrically characterized for the whole image (3000km wide), and atmospheric correction can always be achieved with an error better than 0.5 deg K when accurate data of coincident atmospheric profiles is used. At the worst, when there are no such radiosoundings, SST can be determined with a standard error of estimate of 1.1 deg K (compared with split-window technique) or 1.3 deg K (compared with in situ data).

ISSN:0143-1161    

DOI:10.1080/014311697218098

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

There are different methods for geometric correction of NOAA AVHRR data, but these methods either pay less attention to the accuracy, or are technically complex, almost unsuitable for most users. To combine AVHRR data with other high spatial resolution satellite data, or with ancillary data in GIS, it is necessary to develop an accurate geometric correction method, which should be easy to use even for non-professional users. After analysing the pixel shape and size of AVHRR 1B data along scan line and evaluating the quality of geographical data of NOAA AVHRR 1B data set, we found that the geographical data was adequately accurate for identifying the pixel size and shape and the method was developed accordingly. The proposed method has two steps. The first step is to correct pixel distortion. The separate program performs the distortion correction, applying the geographical data of AVHRR 1B data set to assigning the value of each pixel of the desired output geographical area with given pixel size, and making logical judgment for unassigned pixel. The second step is to perform conventional polynomial transformation on the results of the first step. An application of this method is presented in the paper. To examine the precision, SAVI images derived from the geometrically corrected NOAA AVHRR band image were used to perform overlay with each other and also with a 1 :50000 river system map. A half-pixel accuracy was achieved.

ISSN:0143-1161    

DOI:10.1080/014311697218106

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Measurements have been made of acoustic back-scattering intensity for the vertical and tilted sodar antennae in the convective atmosphere as a function of both zenith and azimuth. Variations in back-scattered intensity have been seen as observed earlier for nocturnal stable conditions. Small-scale anisotropic inhomogeneities in the turbulent thermal structure of the atmospheric boundary layer are considered to be reponsible for the observed anomalous behaviour in acoustic back-scattering.

ISSN:0143-1161    

DOI:10.1080/014311697218115

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor