ISSN:0143-1161    

DOI:10.1080/01431169308904317

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In calculating sea surface temperatures from thermal infrared data from satellites in an area of sunglint it is necessary to apply a correction to allow for reflected solar infrared radiation. A method for making this correction is proposed and it is based on using the well-known theory of Cox and Munk for thermal infrared wavelengths as well as for visible wavelengths. A simple formula enables the correction to be calculated on a pixel-by-pixel basis throughout the area of sunglint.

ISSN:0143-1161    

DOI:10.1080/01431169308904318

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Several types of problems may occur in analysing observations of the sea surface temperature (SST) provided by different instruments. The measurements may be representations of different variables. In our case, the assumed real SST (in term of bulk temperature) is revealed by in situ measurements. Remotely-sensed images provide a biased SST contaminated by the atmosphere. Moreover the brightness temperature measurement of the sea surface is also questionable because of the temperature gradient in the skin layer. The lack of coincidence in the spatial and temporal locations of these two kinds of observations leads us to consider the problem from a geostatistical point of view. We present the method we used to monitor the NOAA satellite bias and merge in situ measurements and remotely-sensed observations of the SST. In order to perform a complete SST mixed chart, we use in situ data available from the Global Transmission System (GTS) and three NOAA-9 images observed during a time period of five days. First, we process a standard combination of infrared channels on the pixels recognized as cloud free. Secondly, we project in situ data on each image and assume no bias between the two data sets by adjusting a constant added to the multichannel algorithm. Thirdly, we merge the data in a unique file where the data, locations and origins are recorded. Finally, the SST is computed on a regular grid using linear interpolations. Such interpolations are provided by geostatistics and the technique is known as kriging.

ISSN:0143-1161    

DOI:10.1080/01431169308904319

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An inflight calibration for AVHRR visible and near-IR bands is discussed and applied to NOAA-7, NOAA-9 and NOAA-11 from 1981 to 1990. The approach, independent of ground support, relies on three unique earth-atmosphere phenomena: molecular scattering over the ocean for absolute visible band calibration, ocean glint to transfer the calibration from the visible band to the near-IR band, and desert reflectance to monitor, independently, the stability of the visible and near-IR bands. The resulting two calibration methods differ in the brightness range and spectral response of the radiance source (molecular scattering versus desert reflectance). Both methods agreed on calibration deterioration for NOAA-9 of 10 ± 3 per cent in the visible band and 16 ± 2 per cent in the near-IR shortly after launch, and 22 ± 2 per cent in both bands three years later. The ocean method showed an increase of 6 per cent and 9 per cent in the sensitivity of the visible and near-IR bands respectively over the lifetime of NOAA-7. However, the desert method showed a decrease of 10 and 12 per cent, respectively, in the two bands. Possible reasons for the differences between the resultant calibration for NOAA-7 from the two methods are discussed. NOAA-11 was calibrated using the desert radiances only. Its inflight response was lower from the preflight response by 21 per cent in channel 1 and 33 per cent in channel 2, a short time after launch. Recommendations for the absolute calibration of NOAA-7, -9 and -11 are given for channels 1 and 2 as a function of time and are compared with other published AVHRR calibrations. The calibration deterioration results in a change in the vegetation index (NDVI) between 0.0 and 0.09. A simple correction scheme is suggested for uncorrected NOAA-7, -9 and -II NDVI and implications of the calibration ratio on AVHRR remote sensing are discussed.

ISSN:0143-1161    

DOI:10.1080/01431169308904320

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

With the temporal profiles of mean values of ratio vegetation index (RVI) and normalized difference vegetation index (NDVI) and their standard deviations over the crop growth cycle for two districts displaying more than 90 per cent of the area sown under wheat, this article indicates the better sensitivity aspect of RVI as compared to NDVI during emergence-crown root initiation-late tillering-jointing-near flowering stages of the crop growth cycle; and suggests a combined use of RVI and NDVI for crop growth oriented studies. The relative narrowness of the standard deviation of RVI in these early crop growth stages as compared to that for the NDVI suggests that the RVI possesses better information content integration capabilities.

ISSN:0143-1161    

DOI:10.1080/01431169308904321

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Using NOAA satellite Advanced Very High Resolution Radiometer (AVHRR) data over the Ludhiana district (Punjab, India) observing 94-98 per cent of the area sown with wheat during the 1986-87 Rabi crop season, this article presents first an analysis of a correlation coefficients matrix for the different crop growth stages Normalized Difference Vegetation Index (NDVI) and Ratio Vegetation Index (RVI) data sets. Though each stage of crop growth is related to its previous as well as its following crop growth stage, the structure of the relation keeps changing over the crop growth cycle. This article discusses the observed typical scatterogram structures such as bowl shape with horizontal cutoff, horizontal cut-offs at upper portions etc. together with the collateral information on histogram parameters for the data sets used in the scatterograms. The paper also discusses the differential behaviour between NDVI and RVI scatterograms for different crop growth stages.

ISSN:0143-1161    

DOI:10.1080/01431169308904322

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Errors have been analysed for monthly-average downward and net longwave surface fluxes derived on a 5°equal-area grid over the globe using a satellite technique. The parametrized equations used for flux computation were derived from a detailed radiative transfer model. Meteorological data used in this technique are available from the TIROS Operational Vertical Sounder (TOVS) system flown aboard NOAA's operational Sun-synchronous satellites. The data used are for February 1982 from NOAA-6 and NOAA-7 satellites. The errors in the parametrized equations were estimated by comparing their results with those from a detailed radiative transfer model. The errors in the TOVS-derived surface temperature, water vapour burden and cloud cover were estimated by comparing these meteorological parameters with independent measurements obtained from other satellite sources. Analysis of the overall errors shows that the present technique could lead to underestimation of downward fluxes by 5 to 15 Wm-2and net fluxes by 4 to 12 Wm-2.

ISSN:0143-1161    

DOI:10.1080/01431169308904323

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Three techniques for the estimate of rain rate from infrared satellite images have been examined and modified to be used over the western Mediterranean Sea. An attempt to optimize these techniques has been made by comparing the remotely-sensed precipitation within situdata, obtained from the rain gauge network over Sardinia, for three different seasons of 1988.

ISSN:0143-1161    

DOI:10.1080/01431169308904324

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Abstract The basic remotely-sensed signal is a parameter defined on the soil surface. This signal, mathematically represented by a function of two space variables, is measured by sensors, at different resolutions. Many applications consist in counting pixels where the measured signal exceeds a given threshold and calculate the percentage of these pixels. This percentage is used to quantify the parameter in question. For example, the quantification of vegetation is often made in this way, the surface parameter being the NDVI. By doing so, one implicitly assumes that this percentage corresponds to the quantification of the parameter at the soil level, and, does not then depend on the sensor resolution.

ISSN:0143-1161    

DOI:10.1080/01431169308904325

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The efficacy of conventional remotely-sensed satellite imagery for regional geological mapping is greatly reduced in northern Ireland due to the extensive vegetation cover. Imagery produced from digitally processed geophysical data sets is an extremely powerful technique for the acquisition of geological information in such terrain. Directional filtering of gravity and aeromagnetic data allows the major structures to be delineated clearly. Pseudo-illumination from the northwest shows the main Caledonian structures: Tempo-Sixmilecross Lineament; the Omagh Fault; the continuation of the Southern Uplands Fault and the en-échelon character of the Fair Head-Clew Bay Lineament. A synergistic display of the geophysical data sets shows the major lithological boundaries, variations within individual lithologies and subsurface geological features.

ISSN:0143-1161    

DOI:10.1080/01431169308904326

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor