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821.
A field experiment was conducted on wheat at New Delhi with five treatments of Nitrogen (N) fertilizer application (0, 30,
60, 90 and 120 kgha-1). Relationship has been established between observed leaf area index (LAI) and remotely sensed vegetation indices. These
relationships are inverted and used for predicting LAI from vegetation indices on different days after sowing. The “re-initialization”
strategy is implemented in model WTGROWS in which initial conditions of model are changed so that the model simulated LAI
match remote sensing predicted LAI. The model performance with re-initialization has been evaluated by comparing the simulated
grain yield and total above-ground dry matter (TDM) values with the actual observations. The results show that in-season re-initialization
is effective in model course correction by improving the simulated results of yield and TDM for different N treatments even
though the model was run with no N stress condition. Model re-initialization at different days shows that the closer is the
day of re-initialization to crop anthesis the more effective is model course correction. Also, the treatment showing maximum
error in yield simulation without re-initialization shows maximum reduction in error by re-initialization. The approach shows
that the remote sensing inputs can substitute for some of the inputs or errors in inputs required by crop models for yield
prediction. 相似文献
822.
B. K. Bhattacharya V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2005,33(2):331-338
The retrieval of land (soil-vegetation complex) surface temperature (LST) was carried out over semi-arid mixed agriculture
landscape of Gujarat using thermal bands (channel 4 and 5) and ground emissivity from atmospherically corrected NDVI of NOAA
AVHRR LAC images. The atmospheric correction of Visible and NIR band reflectance was done using SMAC model. The LST computed
from split-window method and subsequently corrected with fractional vegetation cover were then compared with near synchronous
ground observations of soil and air temperatures made during 13–17 January and April, 1997 at five Land Surface Processes
Experiment (LASPEX) sites of Anand, Sanand, Derol, Arnej and Khandha covering 100 km x 100 km. The fractional vegetation cover
corrected LST at noon hrs. varied from 301.6 – 311.9K in January and from 315.8 – 325.6K in April. The LSTcorr were found to lie in the mid way between AT and ST during January. But in April, LST were found to be more close to ST which
may be due to relatively poor vegetation growth as indicated by lower NDVI values in April indicating more contribution to
LST from exposed soil surface. 相似文献
823.
S. P. Vyas M. D. Steven K. W. Jaggard 《Journal of the Indian Society of Remote Sensing》2005,33(2):315-321
The present work was aimed to compare the abilities of radar and optical satellite data to estimate crop canopy cover, which
is a key component of productivity estimates. Three ERS-1 SAR images were obtained of East Anglia (UK) in 1995 and one ERS-2
SAR image in 1996. The images covered a study area around the IACR Brooms Barn Sugar Beet Research Institute. Field data comprising
radiometric and biophysical measurements of the crop canopy were collected in two fields from June 22 to August 3, 1995 to
coincide with ERS-1 SAR overpass dates. In 1996, field data were collected in two fields from June 11 to July 29 on a weekly
basis. A previously calibrated version of the water cloud model was inverted to estimate Leaf Area Index (LAI) from ERS-1
and ERS-2 SAR backscatter and soil moisture samples. Canopy cover was estimated from the radar-estimated LAI using a standard
exponential relationship that has a well-established coefficient for sugar beet.
Radio-metrically and atmospherically corrected data from three SPOT images in 1995 and one SPOT image in 1996 were used to
calculate the Optimised Soil Adjusted Vegetation Index (OSAVI), from which crop canopy cover was estimated using a relationship
determined previously by canopy modelling. The crop cover values estimated by satellite were in good agreement with those
measured on ground with the Parkinson radiometer. Radar data may be able to provide useful estimates of canopy cover for crop
production modelling, especially in the case of loss of optical data due to cloud. 相似文献
824.
Check dam positioning by prioritization of micro-watersheds using SYI model and morphometric analysis — Remote sensing and GIS perspective 总被引:5,自引:0,他引:5
K. Nooka Ratnam Y. K. Srivastava V. Venkateswara Rao E. Amminedu K. S. R. Murthy 《Journal of the Indian Society of Remote Sensing》2005,33(1):25-38
Sediment Yield Index (SYI) model and results of morphometric analysis have been used to prioritize watersheds and to locate
sites for checkdam positioning in Tarafeni watershed in Midnapur district. West Bengal. Various thematic maps such as land
use/land cover, slope, drainage, soil etc. were prepared from 1RS ID LISS III digital data, SOI toposheets of 1:50,000 scale
and other reference maps. Morphometric parameters such as bifurcation ratio (Rb). drainage density (Dd), texture ratio (T), length of overland flow (Lo), stream frequency (Fu), compactness coefficient (Cc), circularity ratio (Rc), elongation ratio (Er), shape factor (Bs) and form factor (Rf) were computed. Automated demarcation of prioritization of micro-watersheds was done by using GIS overlaying technique by
assigning weight factors to all the identified features in each thematic map and ranks were assigned to the morphometric parameters.
Five categories of priority viz., very high, high, medium, low and very low, were given to all the watersheds in both the
methods. Sixty-two micro-watersheds using SYI method and twenty-three micro-watersheds using morphometric have been prioritized
as very high priority. Final priority map was prepared by considering the commonly occurred very high-prioritized micro-watersheds
in both SYI model and morphometric analysis. Twenty-four suitable sites were identified for check dam construction in 21 highly
prioritized watersheds. It is proved that integrated study of SYI model and morphometric analysis yield good result in prioritization
of watersheds. 相似文献
825.
826.
The reservoir surveys carried out using the conventional equipments like theodolite, plane table, sextant, range finders,
sounding rods, echo-sounders and slow moving boats etc. are time consuming and sometime it takes up to three years to complete
the survey of a major reservoir like Hirakud. During such longtime of survey, the siltation pattern and the bed levels also
get changed. So, the need to update the sediment measurement techniques and to introduce latest technology available in the
field was felt to overcome the difficulties faced in the conventional method especially in major reservoirs. With this objective,
the present study of the assessment of the sedimentation in Linganmakki reservoir is carried out using remote sensing and
GIS techniques. The revised capacities in the zone of reservoir levels (533.05 – 548.78 m) for the year 1989–1990 and 2001–2002
in the zone of 532.20 – 545.91 m of reservoir levels were determined, which is found 2837.84 M cum and 2207.95 M cum respectively.
Based on these results, the sedimentation rates in the zone (533.05 – 548.78 m) come out to be 8.96 ham/100 km2/year and for the zone (532.20 – 545.91 m) is 8.57 ha-m/100 km2/year. It is found that the results are comparable during and the uniform sediment rate of 8.57 ha-m/100 km2/ year can be considered. 相似文献
827.
Summary
A simple model is devised to simulate the turbulent exchange of humidity between ice-supersaturated regions in the upper troposphere
and their subsaturated environment. The model works as a random version of a 2-dimensional cellular automaton, and does not
contain dynamics nor microphysics. In spite of its simplicity the model helps to interpret certain stochastic properties of
ice-supersaturated regions, namely the exponential distribution of the degree of supersaturation and the Weibull distribution
of path-lengths through these regions. In particular, the exponential distribution of the degree of supersaturation evolves
from permanent humidity exchange in spite of a rather peculiar initial distribution of supersaturation, that is, two Dirac
delta functions. Such a robust feature is advantageous for future parameterisations of ISSRs for large-scale models.
Received October 19, 2000 Revised June 25, 2001 相似文献
828.
W. R. Skinner M. D. Flannigan B. J. Stocks D. L. Martell B. M. Wotton J. B. Todd J. A. Mason K. A. Logan E. M. Bosch 《Theoretical and Applied Climatology》2002,71(3-4):157-169
Summary
In Canada, the average annual area of burned forest has increased from around 1 million ha in the 1970’s to over 2.5 million
ha in the 1990’s. A previous study has identified the link between anomalous mid-tropospheric circulation at 500 hPa over
northern North America and wildland fire severity activity in various large regions of Canada over the entire May to August
fire season. In this study, a northern North American study region of the hemispheric gridded 5° latitude by 10° longitude
500 hPa dataset is identified and analysed from 1959 to 1996 for a sequence of six monthly periods through the fire season,
beginning in April and ending in September. Synoptic types, or modes of upper air behavior, are determined objectively by
the eigenvector method employing K-means cluster analysis. Monthly burned areas from the Canadian Large Fire Database (LFDB)
for the same period, 1959 to 1996, are analysed in conjunction with the classified monthly 500 hPa synoptic types. Relationships
between common monthly patterns of anomalous upper flow and spatial patterns of large fire occurrence are examined at the
ecozone level. Average occurrence of a monthly synoptic type associated with very large area burned is approximately 18% of
the years from 1959 to 1996. The largest areas burned during the main fire (May to August) season occur in the western Boreal
and Taiga ecozones – the Taiga Plains, Taiga Shield, Boreal West Shield and Boreal Plains. Monthly burned areas are also analysed
temporally in conjunction with a calculated monthly zonal index (Zim) for two separate areas defined to cover western and eastern Canada. In both western and eastern Canada, high area burned
is associated with synoptic types with mid-tropospheric ridging in the proximity of the affected region and low Zim with weak westerlies and strong meridional flow over western Canada.
Received April 3, 2001 Revised July 13, 2001 相似文献
829.
Summary ?Microclimatological data obtained during a field experiment in the nongrowing winter period were used to study the microclimatologically
stable night conditions of a 200 × 150 m miscanthus (Miscanthus cv. giganteus) stand and compared to open field conditions. The microclimatological pattern within the miscanthus canopy
was characterized by long-wave radiative cooling of the plant stand and by an established temperature inversion within the
canopy at calm nights. The results show that there are significant differences in air temperature and energy balance components
between the open field and the miscanthus field during calm and clear nights. In general, net radiation difference during
the cold and calm nights was relatively constant and about 20 W m−2 less negative in miscanthus (because of lower surface temperatures) than at the open field. Air temperature differences also
remained fairly constant and were up to 3 °C lower than at the open field (at the height of 1 m). Through thermal inversion
cold air accumulated in the lower parts of the canopy as shown by the vertical air temperature profiles. They showed a greater
amplitude within the diurnal cycle in the miscanthus stand than in the open field. Through the onset of wind, temperature
profiles changed rapidly and differences diminished. Vertical katabatic air drainage into the canopy layers was estimated
indirectly by using the energy balance approach. It was calculated from the significant energy balance closure gap and showed
a mean air exchange rate of up to 22 m3 m−2 h−1, related to a stand volume of 1 m2 area and 4 m height, during the mostly calm and clear nights, depending on the canopy net radiation and turbulent heat exchange
forced by slight wind spells. Quantitative uncertainties in calculated cold air drainage which are introduced by the measurement
method and certain assumptions in the calculations, were considered in a sensitivity analysis. In spite of these uncertainties
evidence of katabatic cold air flow is given.
Received July 29, 1999; revised June 11, 2001; accepted March 14, 2002 相似文献
830.
Townsend's hypothesis states that turbulence near a wall can be divided into an activepart that transports momentum, and an inactive part that does not, and that these twokinds of turbulence do not interact. Active turbulence is generated by wind shear and has properties that scale on local parameters of the flow, while inactive turbulence isthe product of energetic processes remote from the surface and scales on outer-layerparameters. Both kinds of motion can be observed in the atmospheric surface layer, soMonin–Obukhov similarity theory, which is framed in terms of local parameters only,can apply only to active motions. If Townsend's hypothesis were wrong, so that activeand inactive motions do interact in some significant way, then transport processes nearthe ground would be sensitive to outer-layer parameters such as boundary-layer depth,and Monin–Obukhov theory would fail.Experimental results have shown that heat transport near the ground does depend onprocesses in the outer layer. We propose a mechanism for this whereby inactive motionsinitiate active, coherent ejection/sweep structures that carry much of the momentum andheat. We give evidence that the inactive motions take the form of streak patterns of fasterand slower air, and argue that these are induced by the pressure effects of large eddiespassing overhead. The streak pattern includes regions where faster streams of air overtakeand engulf slower-moving streaks. Transverse vortices form across the spines of the streaksat these places and some of them develop into horseshoe vortices. These horseshoe vorticesgrow rapidly and are rotated forward in the sheared flow so they soon contact the ground,squirting the air confined between the legs of the horseshoe vortex outwards as a forcefulejection. This model is consistent with a wide range of results from the field and laboratoryexperiments. Heat transport is significantly affected, so undermining the dimensionalassumptions of Monin–Obukhov similarity theory. 相似文献