摘要:

Inter-state disputes on water utilization from the Cauvery river have necessitated an accurate and timely estimate of the irrigated crop area in each season to optimise the water supply through the canal system and to suggest a departure from the traditional system of protective kharif irrigation to productive rabi irrigation. An inventory of the cropland in the command area of Krishnarajasagar Project was made by visually interpreting satellite imagery. Satellite data showed a reduction of about 6 per cent in the irrigated area from 1973 to 1986. Effect of scale of imagery and percentage of boundary pixels on accuracy of estimated irrigated area was studied. 1:250000 scale was found to be adequate for this large command area. The accuracy of estimated irrigated crop area was within 5 per cent of the DES estimate for the entire command area. At taluk-level, total enumeration gave an overestimate of irrigated area by 13 per cent compared to an overestimation of about 18 per cent using multistage-proportionate-probability sampling with a grid size of 2-5 km by 2-5 km. The per hectare cost of estimating the crop land using satellite remote sensing was found to be two to five times cheaper than the conventional system. An attempt was also made to evaluate various vegetation indices derived from Landsat-TM for identifying irrigated croplands and IRS-1A/LISS-II data for identification of crop types. It was concluded, from the results of this study, that satellite remote sensing is an effective time saving techqniue for providing seasonal assessment of irrigated cropland in the command areas.

ISSN:0143-1161    

DOI:10.1080/01431169408954162

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The area under wheat was estimated and a forecast of production made in a predominantly un-irrigated region (36 per cent irrigated wheal crop, geographical area 5-61 Mha) of Madhya Pradesh (India) using digital data from LISS-I (Linear Imaging Self Scanner) onboard Indian Remote Sensing Satellite (IRS-IB), for the crop season 1991-92. A stratified sampling approach based on 5 km by 5 km sample segments, 10 per cent sampling fraction in conjunction with supervised maximum likelihood (MXL) classification was used for wheat acreage estimation. Yield forecasts were based on an optimal combination of forecasts from two different methodologies, viz., wheat yield-spectral relationship and time series analysis using ARIMA (Auloregressive Integrated Moving Average) approach. In the former, a two-year (1989-90, 1990-91) pooled regression relating LISS-I derived Near Infrared/Red (NIR/R) radiance ratio to district wheat yields was developed and used to forecast wheat yields for the year 1991-92 based on classified wheat pixels. In the latter case, historical district-wise wheat yield data of 35 years was used to develop appropriate ARIMA models and used to forecast 1991-92 yields. The relative deviation of remotely-sensed-based forecasted production, acreage and yield from the post-harvest estimates released later by the State Department of Agriculture were — 15.8, — 1002 and — 601 per cent, respectively. The acreage and yield meet the accuracy of 85 per cent at 90 and 95 per cent confidence levels, respectively.

ISSN:0143-1161    

DOI:10.1080/01431169408954163

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The tilt modulations of the like- and cross-polarized cross-sections for arbitrarily oriented resolution cells are determined using the unified full-wave approach. A broad family of non-Gaussian rough surfaces characterized by the gamma surface height probability density functions of order K are considered. Furthermore a Pearson-Moskowitz surface height spectral density function is assumed for the sea surface. The surface height autocorrelation function is also assumed to be non-Gaussian. An arbitrarily oriented mean plane associated with the resolution cell is characterized by tilt angles in and perpendicular to a fixed reference plane of incidence. The ‘tilt modulation’ of the scattering cross-sections is determined as functions of the wavelength of the incident field 𝛌0and the backscatter angle 0i0. Each resolution cell represents the real (or synthetic) radar footprint. The size of the resolution cell, orientation, and the statistical characteristics of the non-Gaussian surface determine the radar cross-section. Radar remote sensing options are discussed to distinguish between random rough surfaces characterized by different probability density functions.

ISSN:0143-1161    

DOI:10.1080/01431169408954164

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431169408954165

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431169408954166

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Significant sources of uncertainty in global trace gas budgets are due to lack of knowledge concerning the areal and temporal extent of source and sink areas. Synthetic aperture radar (SAR) is particularly suited to studies of northern ecosystems because of its all-weather operating capability which enables the acquisition of seasonal data. As key controls on methane exchange, the ability to differentiate major vegetation communities, inundation, and leaf area index (LAI) with satellite and airborne SAR data would increase the accuracy and precision of regional and seasonal estimates of methane exchange. The utility of SAR data for monitoring key controls on methane emissions from Arctic and boreal ecosystems is examined.

ISSN:0143-1161    

DOI:10.1080/01431169408954167

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Under typical field conditions of green vegetation over a dark soil, vegetation indices have been shown to vary in a near-linear fashion with the fraction of absorbed photosynthetically active radiation (APAR). On the basis of model results the AVHRR/2 sensor, which was not designed originally to make biophysical measurements, provides the best match to criteria for producing a near-linear variation of vegetation indices with APAR. The radiance measured by the AVHRR/2 sensor, however, is highly sensitive to atmospheric conditions. In the near future sensors will be launched which have been designed with biophysical imaging as an important criterion. This letter examines the potential of three of these new sensors for estimating APAR. Scattering coefficients calculated for each sensor are shown to provide poor simulation of the pholosyn-thetic action efficiency of photosynthesis. Using the combined visible wavebands to calculate the scattering coefficients, however, produce values that are comparable with AVHRR/2.

ISSN:0143-1161    

DOI:10.1080/01431169408954168

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This letter presents results of experiments conducted to assess the use of linear mixing models to unmix the reflectance spectra of water. The model was tested with 11 reflectance spectra measured at Tucurui reservoir, Brazilian Amazon. The results showed that the fraction of chlorophyll reflectance accounting for the reflectance spectra of the various samples correlate significantly with the chlorophyll concentration in the 600 to 700 nm spectral region.

ISSN:0143-1161    

DOI:10.1080/01431169408954169

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The loss of Landsat 6, at launch, and the ageing sensors on board Landsats 4 and 5, enhance the value of existing TM images. This letter shows that 88 per cent of Britain was imaged as cloud-free scenes or quarter scenes, in both the summer and winter of 1988-1990 and 97.5 per cent was imaged on at least one date. Acquisitions in 1991-1993 have been few.

ISSN:0143-1161    

DOI:10.1080/01431169408954170

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor