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31.
Trend analysis of evapotranspiration over India: Observed from long-term satellite measurements 总被引:1,自引:0,他引:1
Sheshakumar Goroshi Rohit Pradhan Raghavendra P Singh K K Singh Jai Singh Parihar 《Journal of Earth System Science》2017,126(8):113
Owing to the lack of consistent spatial time series data on actual evapotranspiration (ET), very few studies have been conducted on the long-term trend and variability in ET at a national scale over the Indian subcontinent. The present study uses biome specific ET data derived from NOAA satellite’s advanced very high resolution radiometer to investigate the trends and variability in ET over India from 1983 to 2006. Trend analysis using the non-parametric Mann–Kendall test showed that the domain average ET decreased during the period at a rate of \(0.22\,\hbox {mm year}^{-1}\). A strong decreasing trend (\(m = -1.75\, \hbox {mm year}^{-1}\), \(F = 17.41\), \(P\) 0.01) was observed in forest regions. Seasonal analyses indicated a decreasing trend during southwest summer monsoon (\(m= -0.320\, \hbox {mm season}^{-1}\,\hbox {year}^{-1})\) and post-monsoon period (\(m= -0.188\, \hbox {mm season}^{-1 }\,\hbox {year}^{-1})\). In contrast, an increasing trend was observed during northeast winter monsoon (\(m = 0.156 \,\hbox {mm season}^{-1 }\,\hbox {year}^{-1})\) and pre-monsoon (\(m = 0.068\, \hbox {mm season}^{-1 }\,\hbox {year}^{-1})\) periods. Despite an overall net decline in the country, a considerable increase ( \(4 \,\hbox {mm year}^{-1}\)) was observed over arid and semi-arid regions. Grid level correlation with various climatic parameters exhibited a strong positive correlation (\(r \!>\!0.5\)) of ET with soil moisture and precipitation over semi-arid and arid regions, whereas a negative correlation (\(r\) \(-0.5\)) occurred with temperature and insolation in dry regions of western India. The results of this analysis are useful for understanding regional ET dynamics and its relationship with various climatic parameters over India. Future studies on the effects of ET changes on the hydrological cycle, carbon cycle, and energy partitioning are needed to account for the feedbacks to the climate. 相似文献
32.
M. G. Raghavendra Reddy G. P. Obi Reddy A. K. Maji K. Nageshwara Rao 《Journal of the Indian Society of Remote Sensing》2003,31(4):271-282
In the present study, an attempt has been made to analyse IRS-ID LISS-III satellite data in conjunction with field observations
for geomorphological mapping and pedo-geomorphological characterisation in Mohgaon area of Nagpur district, Maharashtra. Analysis
of satellite data reveals distint geomorphological units viz., plateau top, isolated mounds, linear ridges, escarpments, plateau
spurs, subdued plateau, rolling plains, pediments, narrow valleys and main valley floor. Soil profiles, studied on different
identified landforms, showed variation in site and morphological charactaristics. Moderate soil erosion occurs on plateau
top, isolated mouds, plateau spurs, rollinmg plains and pediments. Severe erosion was identified on escarpments and subdued
plateau and narrow valleys suffer very slight erosional hazards. Moderately well drained soils were found on rolling plains,
pediments, narrow valleys and main valley floor. Well drained soils were noticed on plateau top and plateau spurs. Very shallow
soils were found on the plateau top and isolated mounds. Shallow soils are found in linear ridges, escarpments, plateau spurs
and rolling plains. Moderately deep and deep soils are found on subdued plateau, pediments and main valley floor. The landform-soil
relatioinship reveals that the soils on the plateau top and isolated mounds are very shallow, well drained, clay textured.
The soils on the narrow valleys and main valley floor are deep, moderatly well drained, and clayey in texture. It also indicates
that landform-soil processes are governed by physiographic position, drainage, slope and erosion conditions of the area. The
present study reveals that the analysis of remotely sensed data in conjunction with field observations in GIS will be of immense
help in geomorphology mapping, analysis of landform-soil relationships and generation of their geo-spatial database. 相似文献
33.
Simulation of a Himalayan cloudburst event 总被引:5,自引:0,他引:5
Someshwar Das Raghavendra Ashrit M. W. Moncrieff 《Journal of Earth System Science》2006,115(3):299-313
Intense rainfall often leads to floods and landslides in the Himalayan region even with rainfall amounts that are considered
comparatively moderate over the plains; for example, ‘cloudbursts’, which are devastating convective phenomena producing sudden
high-intensity rainfall (∼10 cm per hour) over a small area. Early prediction and warning of such severe local weather systems
is crucial to mitigate societal impact arising from the accompanying flash floods. We examine a cloudburst event in the Himalayan
region at Shillagarh village in the early hours of 16 July 2003. The storm lasted for less than half an hour, followed by
flash floods that affected hundreds of people. We examine the fidelity of MM5 configured with multiple-nested domains (81,
27, 9 and 3 km grid-resolution) for predicting a cloudburst event with attention to horizontal resolution and the cloud microphysics
parameterization. The MM5 model predicts the rainfall amount 24 hours in advance. However, the location of the cloudburst
is displaced by tens of kilometers 相似文献
34.
Raghavendra Hemant Bhalerao Shirish S. Gedam 《Journal of the Indian Society of Remote Sensing》2018,46(11):1841-1852
Local stereo matching algorithms use winner-take-all approach to get the disparity. Many times they end up at an erroneous result. To solve this, in the present work, a novel stereo image matching technique has been developed that identifies the most likely local minimum from the several possible local minima that corresponds to true disparity. The technique uses properties of the physical continuity of the land surface by the watershed lines applied to the disparity space volume. This helps to minimize the search for the most probable local minima as the correct solution for the matching. The matching is further improved by combining the watershed lines of disparity space volume of two stereo pairs from the tri-stereo. In the present study, experiments have been carried out using the standard Middlebury stereo datasets and remotely sensed tri-stereo images. Based on this approach, the experiments are successfully carried out using the test dataset. The experimental results are compared with the results from the currently contemporary techniques of dynamic programming and semi-global matching which resulted in 2–10% improvement in density of matched points for different datasets. 相似文献
35.
36.
Raghavendra Krishnamurthy Ronald Calhoun Harindra Fernando 《Boundary-Layer Meteorology》2010,136(1):45-57
Accurate estimation of dissipation rate is important in understanding and analyzing turbulent flows found in environment and
engineering processes. Many previous studies have focused on measuring the local dissipation rate at a single point or averaged
dissipation rate over a suitable area. Since coherent Doppler lidar is capable of providing multi-point measurements covering
a large spatial extent, it is well-suited for examining the distribution of dissipation in the atmosphere. In this paper,
an approach is presented that is based on retrieving the dissipation rate from coherent Doppler lidar data using large-eddy
simulation. Two Coherent Doppler lidars performed range height indicator (RHI) scans of a vertical/cross-barrier plane during
the Terrain-induced Rotor Experiment (T-REX). Two-dimensional velocity vectors were retrieved using a least squares method.
The velocity vectors retrieved from co-planar RHI scans are used to estimate subgrid scale (SGS) quantities through a known
SGS parameterization. For the T-REX datasets analyzed, the dissipation rate was found to increase in the presence of rotors,
subrotors, and, as expected, in regions of high wind shear. Owing to the presence of sharper gradients in subrotors, their
dissipation rate is generally larger than that of rotors. 相似文献
37.
R. R. Reddy K. Rama Gopal L. Siva Sankara Reddy K. Narasimhulu K. Raghavendra Kumar Y. Nazeer Ahammed C. V. Krishna Reddy 《Journal of Atmospheric Chemistry》2008,59(1):47-59
In the present study, an attempt has been made to examine the governing photochemical processes of surface ozone (O3) formation in rural site. For this purpose, measurements of surface ozone and selected meteorological parameters have been
made at Anantapur (14.62°N, 77.65°E, 331 m asl), a semi-arid zone in India from January 2002 to December 2003. The annual
average diurnal variation of O3 shows maximum concentration 46 ppbv at noon and minimum 25 ppbv in the morning with 1σ standard deviation. The average seasonal
variation of ozone mixing ratios are observed to be maximum (about 60 ppbv) during summer and minimum (about 22 ppbv) in the
monsoon period. The monthly daytime and nighttime average surface ozone concentration shows a maximum (55 ± 7 ppbv; 37 ± 7.3 ppbv)
in March and minimum (28 ± 3.4 ppbv; 22 ± 2.3 ppbv) in August during the study period. The monthly average high (low) O3 48.9 ± 7.7 ppbv (26.2 ± 3.5 ppbv) observed at noon in March (August) is due to the possible increase in precursor gas concentration
by anthropogenic activity and the influence of meteorological parameters. The rate of increase of surface ozone is high (1.52 ppbv/h)
in March and lower (0.40 ppbv/h) in July. The average rate of increase of O3 from midnight to midday is 1 ppbv/h. Surface temperature is highest (43–44°C) during March and April months leading to higher
photochemical production. On the other hand, relative humidity, which is higher during the rainy season, shows negative correlation
with temperature and ozone mixing ratio. It can be seen that among the two parameters are measured, correlation of surface
ozone with wind speed is better (R
2=0.84) in compare with relative humidity (R
2=0.66). 相似文献
38.
Sujay Dutta Suresh K. Singh Sushma Panigrahy 《Journal of the Indian Society of Remote Sensing》2014,42(2):353-361
Remote sensing technology becomes an effective and inexpensive technique for detecting disease in vegetation. In this study, an attempt has been done to discriminate healthy and late blight affected crop using remote sensing based indices such as NDVI and LSWI. NDVI and LSWI spectral profiles between healthy and late blight affected crop shows large difference. Mean difference in reflectance between two acquired dates Jan. 10 and 29, 2009 crop clusters varied from 31.28 % in red band, 7.7 % in NIR band and 6.23 % in SWIR bands in healthy crops while in late blight affected crops it is ?15.5 % in red, 44.4 % in NIR and ?14.61 % in SWIR bands. Negative percentage differences in reflectance indicate reflectance increases from Jan. 10, 2009 to Jan. 29, 2009, while positive difference indicate decrease in reflectance between the two dates. Since potato is an irrigated crop, these differences in reflectance are attributed to prevalent disease at that time. It is found that severely affected areas are Bardhman, Arambag, Bishnupur, Ghatal and Hugli taluka with crop damage areas are 4036.66, 1138.68, 2025.23, 469.15, and 380.08 ha, respectively. 相似文献
39.
Dalia Bach Kirschbaum Robert Adler Yang Hong Sujay Kumar Christa Peters-Lidard Arthur Lerner-Lam 《Environmental Earth Sciences》2012,66(6):1683-1696
The increasing availability of remotely sensed data offers a new opportunity to address landslide hazard assessment at larger
spatial scales. A prototype global satellite-based landslide hazard algorithm has been developed to identify areas that may
experience landslide activity. This system combines a calculation of static landslide susceptibility with satellite-derived
rainfall estimates and uses a threshold approach to generate a set of ‘nowcasts’ that classify potentially hazardous areas.
A recent evaluation of this algorithm framework found that while this tool represents an important first step in larger-scale
near real-time landslide hazard assessment efforts, it requires several modifications before it can be fully realized as an
operational tool. This study draws upon a prior work’s recommendations to develop a new approach for considering landslide
susceptibility and hazard at the regional scale. This case study calculates a regional susceptibility map using remotely sensed
and in situ information and a database of landslides triggered by Hurricane Mitch in 1998 over four countries in Central America.
The susceptibility map is evaluated with a regional rainfall intensity–duration triggering threshold and results are compared
with the global algorithm framework for the same event. Evaluation of this regional system suggests that this empirically
based approach provides one plausible way to approach some of the data and resolution issues identified in the global assessment.
The presented methodology is straightforward to implement, improves upon the global approach, and allows for results to be
transferable between regions. The results also highlight several remaining challenges, including the empirical nature of the
algorithm framework and adequate information for algorithm validation. Conclusions suggest that integrating additional triggering
factors such as soil moisture may help to improve algorithm performance accuracy. The regional algorithm scenario represents
an important step forward in advancing regional and global-scale landslide hazard assessment. 相似文献
40.
Various analytical expressions describing the hydraulic behavior of a continuous permeable reactive barrier (PRB) are developed based upon a two-dimensional approximation of the local groundwater flow system. The fully penetrating PRB is represented as an arbitrarily oriented elliptical “analytic element” with a hydraulic conductivity different from that of the aquifer. The validity of this elliptical geometry approximation as a surrogate for rectangular PRB performance is evaluated and put into context. Closed-form expressions for solute travel time distributions along the extent of the barrier and PRB capture zone geometry are evaluated for general barrier dimension (length and width), hydraulic conductivity, and orientation with respect to regional flow. These expressions are used as the foundation of a simple PRB design process, and provide some interesting insights into the hydraulic behavior of continuous permeable reactive barriers. 相似文献