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Enhanced urban landcover classification for operational change detection study using very high resolution remote sensing data
Get PDFThis study presents an operational case of advancements in urban land cover classification and change detection by using very high resolution spatial and multispectral information from 4-band QuickBird (QB) and 8-band WorldView-2 (WV-2) image sequence. Our study accentuates quantitative, pixel based, image difference approach for operational change detection using very high resolution pansharpened QB and WV-2 images captured over San Francisco city, California, USA (37° 44" 30N', 122° 31" 30' W and 37° 41" 30'N,122° 20" 30' W). In addition to standard QB image, we compiled three multiband images from eight pansharpened WV-2 bands: (1) multiband image from four traditional spectral bands, i.e., Blue, Green, Red and near-infrared 1 (NIR1) (henceforth referred as "QB equivalent WV-2"), (2) multiband image from four new spectral bands, i.e., Coastal, Yellow, Red Edge and NIR2 (henceforth referred as "new band WV-2"), and (3) multiband image consisting of four traditional and four new bands (henceforth referred as "standard WV-2"). All the four multiband images were classified using support vector machine (SVM) classifier into four most abundant land cover classes, viz, hard surface, vegetation, water and shadow. The assessment of classification accuracy was performed using random selection of 356 test points. Land cover classifications on "standard QB" image (kappa coeffiecient, κ = 0.93), "QB equivalent WV-2" image (κ = 0.97), and "new band WV-2" image (κ = 0.97) yielded overall accuracies of 96.31, 98.03 and 98.31, respectively, while "standard WV-2" image (κ = 0.99) yielded an improved overall accuracy of 99.18. It is concluded that the addition of four new spectral bands to the existing four traditional bands improved the discrimination of land cover targets, due to increase in the spectral characteristics of WV-2 satellite. Consequently, to test the validity of improvement in classification process for implementation in operational change detection application, comparative assessment of transition of various landcover classes in three WV-2 images with respect to "standard QB" image was carried out using image difference method. As far as waterbody class is concerned, there was no significant transition observed in all the three WorldView-2 Images, whereas, hard surface class showed lowest transition in "standard WV-2" image and highest in case of "new band WV-2". The most significant transition was occurred in vegetation class in all of the three images, showing positive change (increase) in standard WV-2 image (0.31 Sq. Km) and negative change (decrease) in other two images (-0.12 Sq. Km for "QB equivalent WV-2" image and -31.15 Sq. Km in "new band WV-2" image) with considerable amount. Similar case was observed with the shadow class, but the difference is, transition from shadow to other classes was negative in all the three WV-2 images which can be attributed to the fact that, "standard QB" image had more shadow area (based on acquisition time and sun position) than WV-2, that means all the band combinations of WV-2 succeeded in extracting the features hidden below the shadow in "standard QB" image. These trends indicate that the overall bandwise transition in landcover classes in case of "standard WV-2" is more precise than other two images. We note that "QB equivalent WV-2" image had narrower band widths than those of "standard QB" image but the observed vegetation change is not prominent as in case of other two images, but at the same time, transition in hard surface and waterbody was discerned more efficiently than "new band WV-2" image. The addition of new bands in WV-2 enabled more effective vegetation analysis, so the vegetation transition results shown by "new band WV-2" image were at par with the "standard WV-2" image, showing the importance of these newly added bands in the WV-2 imagery, with comparatively lower transitions in other classes. In a nutshell, it can be claimed that incorporation of new bands along with even narrower Red, Green, Blue and Near Infrared-1 bands in WV-2 image holds remarkable importance which leads to enhancement in the potential of WV-2 imagery in change detection and other feature extraction studies
Optical exploration of biomass burning aerosols over a high-altitude station by combining ground-based and satellite data
No full textDynamical Seasonal Prediction of Indian Summer Monsoon using AGCM: Weighted Ensemble Mean Approach
Get PDFThis study examines the fidelity of portable unified model's Atmospheric General Circulation Model in ensemble seasonal prediction of Indian Summer Monsoons of 1999-2004, driven by May SST anomaly persistent boundary conditions. Simple Ensemble-mean (EM) is inappropriate due to the presence of large deviation among the ensemble members in simulation of Indian Summer Monsoon Rainfall (ISMR). Thus 'Weighted Ensemble Mean' (WEM) method is used in the present study. In WEM method, weights are determined for all ensemble members at each model grid point using daily precipitation anomaly to distinguish the most reliable members and outliers among the ensemble members. Ensemble-mean then obtained by weighted combinations of all ensemble members is referred as 'Weighted Ensemble Mean'. The WEM prediction of ISMR better matches with observations than EM in majority of the monsoons. Further, WEM estimated using monthly and seasonal mean weights are assessed with respect to WEM from daily mean weights. WEM with monthly/seasonal weighting is found to be similar to EM in most of the monsoons and hence daily weighting is more suited approach than monthly/seasonal weighting
PM2.5 chemical source profiles of emissions resulting from industrial and domestic burning activities in India
Get PDFA study has been performed to develop PM2.5 (particles with aerodynamic diameters ≤ 2.5) chemically speciated source profiles of different industrial and domestic burning practices in India. A total of fifty-five PM2.5 samples have been collected in emissions resulting from (1) industrial furnaces, (2) household fuels, (3) municipal solid waste burning, and (4) welding workshop burning practices, and categorized for eleven subtypes of sources. The collected samples were subjected to chemical analysis for twenty-one elemental (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Ni, Pb, S, Sb, Se, V, Zn), nine ionic (Na+, K+, Mg2+, Ca2+, NH4+, Cl–, F–, NO3–, SO42–), OC, and EC source indicator species using atomic absorption spectrometry, ion chromatography and carbon analysis (thermal/optical transmittance method), respectively. The carbonaceous fraction was most abundant in household fuel burning emissions (47.6 ± 7.45% to 65.92 ± 13.13%). The ionic/elemental ratios of major inorganic constituents (Ca2+/Ca, Mg2+/Mg and Na+/Na) have been identified to describe the PM2.5 emissions from combustion or re-suspension dusts during industrial activities. Brick Kiln processes (BKP) have been identified as the major emitter of the highest number of toxic species (Cd, Co, Mo, Sb and V), followed by steel re-rolling mills (Hg and Pb) and steel processing industries (As, Ni). The source marker calculations also confirmed that K+, Mn, and As are good markers for biomass burning, metallurgical industrial emission, and coal burning, respectively, similar to the findings in previous studies
Verification of spatio-temporal monsoon rainfall variability across Indian region using NWP model output
No full textEvaluation of weather forecasting systems and assessment of existing verification procedures are essential to achieve desirable seamless rainfall prediction. Prediction of wet and dry spells is quite useful in agriculture and hydrology but very few attempts have been made so far to resolve the issue using numerical model output. Performance of five state-of-the-art global atmospheric general circulation models and their ensemble mean has been examined in predicting the parameters of wet and dry spells (WSs/DSs) during monsoon period of 2008–2011 over seven subzones of the Indian region. The number of WSs across the region is found to be underestimated, while total duration and rainfall amount of WSs (DSs) overestimated (underestimated). Start of the first WS is late and ends of the last WS early in the model forecast. More uncertainty is noticed in the prediction of DS rainfall and its duration than that of the WS. The percentage area of India under wet conditions (rainfall amount over each grid is more than its daily mean monsoon rainfall) and rainwater over the wet area is overestimated by about 59 and 32 %, respectively, in all model
Sensitivity of precipitation to sea surface temperature over the tropical summer monsoon region - and its quantification
No full textOver the tropical oceans, higher sea surface temperatures (SST, above 26 °C) in summer are generally accompanied by increased precipitation. However, it has been argued for the last three decades that, any monotonic increase in precipitation with respect to SST is limited to an upper threshold of 28–29.5 °C, and beyond this, the relationship fails. Based on this assessment it has often been presumed that, since the mean SSTs over the Asian monsoon basins (Indian Ocean and north-west Pacific) are mostly above the threshold, SST does not play an active role on the summer monsoon variability. It also implies that increasing SSTs due to a changing climate need not result in increasing monsoon precipitation. The current study shows that the response of precipitation to SST has a time lag, that too with a spatial variability over the monsoon basins. Taking this lag into account, the results here show that enhanced convection occurs even up to the SST maxima of 31 °C averaged over these basins, challenging any claim of an upper threshold for the SST-convection variability. The study provides us with a novel method to quantify the SST-precipitation relationship. The rate of increase is similar across the basins, with precipitation increasing at ~2 mm day−1 for an increase of 1 °C in SST. This means that even the high SSTs over the monsoon basins do play an active role on the monsoon variability, challenging previous assumptions. Since the response of precipitation to SST variability is visible in a few days, it would also imply that including realistic ocean–atmosphere coupling is crucial even for short term monsoon weather forecasts. Though recent studies suggest a weakening of the monsoon circulation over the last few decades, results here suggest an increased precipitation over the tropical monsoon regions, in a global warming environment with increased SSTs. Thus the signature of SST is found to be significant for the Asian summer monsoon, in a quantifiable manner, seamlessly through all the timescales—from short-term intraseasonal to long-term climate scales
Impact of satellite-retrieved atmospheric temperature profiles assimilation on Asian summer monsoon 2010 simulation
No full textThe impact of assimilation of satellite-retrieved atmospheric temperature profiles data in simulating mean monsoon circulation and rainfall of summer monsoon 2010 is examined in this study using the regional climate model, Weather Research and Forecasting model (WRF). Two experiments are performed; the first one is the control experiment (WRF-CTL) where no assimilation is carried out, and the second one is similar to the first one, but satellite-retrieved atmospheric temperature profiles are assimilated using a four-dimensional data assimilation method (WRF-AIRS). Mean monsoon features such as the low level jet, monsoon trough, tropical easterly jet, meridional pressure gradient and the spatial distribution of rainfall are better simulated in WRF-AIRS. Correlation coefficients between the observed and WRF-AIRS (WRF-CTL) daily zonal wind shear, meridional wind shear and rainfall indices over the Indian summer monsoon region are 0.98, 0.96 and 0.67 (0.32, 0.35 and 0.23), respectively. The zonal and meridional wind indices over the western Pacific and East Asia are 0.9 and 0.8 (0.6 and 0.5), respectively. Spatial distribution of rainfall displays double ITCZ like rainfall pattern over the tropical Indian Ocean in WRF-CTL, whereas WRF-AIRS display a single ITCZ pattern, which is similar to the observed one. The temporal evolution of the vertical structure of temperature (associated with rainfall activity over the monsoon core region) shows warming in the midtroposphere to upper troposphere (by 0.5 to 1.5 °C) and cooling in the midtroposphere to lower troposphere (by 0.5 to 1.0 °C). This atmospheric temperature distribution associated with rainfall is well simulated by WRF-AIRS. Under heavy rainfall conditions, WRF-AIRS produces strong vertical motion consistent with the observations but is absent (or weak) in WRF-CTL. This study deduces that the assimilation of temperature profiles in the regional climate model can significantly improve the dynamical and thermodynamical features of monsoon by representing the vertical distribution of temperature more realistically. Our analysis reiterates that the Asian summer monsoon circulation is mainly controlled by thermal forcing. Our study suggests that it is essential to improve the existing parameterization schemes for better simulation of summer monsoon
Large-scale and spatio-temporal extreme rain events over India: a hydrometeorological study
No full textFrequency, intensity, areal extent (AE) and duration of rain spells during summer monsoon exhibit large intra-seasonal and inter-annual variations. Important features of the monsoon period large-scale wet spells over India have been documented. A main monsoon wet spell (MMWS) occurs over the country from 18 June to 16 September, during which, 26.5 of the area receives rainfall 26.3 mm/day. Detailed characteristics of the MMWS period large-scale extreme rain events (EREs) and spatio-temporal EREs (ST-EREs), each concerning rainfall intensity (RI), AE and rainwater (RW), for 1 to 25 days have been studied using 1° gridded daily rainfall (1951-2007). In EREs, 'same area' (grids) is continuously wet, whereas in ST-EREs, 'any area' on the mean under wet condition for specified durations is considered. For the different extremes, second-degree polynomial gave excellent fit to increase in values from distribution of annual maximum RI and RW series with increase in duration. Fluctuations of RI, AE, RW and date of occurrence (or start) of the EREs and the ST-EREs did not show any significant trend. However, fluctuations of 1° latitude-longitude grid annual and spatial maximum rainfall showed highly significant increasing trend for 1 to 5 days, and unprecedented rains on 26-27 July 2005 over Mumbai could be a realization of this trend. The Asia-India monsoon intensity significantly influences the MMWS RW
Lightning and convective rain study in different parts of India
No full textThe effect of solar variability parameters (solar flux (F10.7cm), cosmic ray flux, sunspot numbers) and meteorological parameters on convective rainfall and lightning flashes in four different Indian regions of equal area is studied. Regions are selected having different topological, vegetation, proximity with ocean and habitat features. Solar variability shows statistically insignificant effect on lightning flash and convective rainfall. The seasonal variation of lightning flashes and convective rainfall in each region could be explained considering the variation of CAPE and surface temperature in that region. The dependence of lightning flashes and convective rainfall on meteorological parameters varies from region to region, as is evident from correlation studies. Lightning flashes is well correlated (R=0.81) with CAPE in region R1 and barely correlated (R=0.23, 0.24) in region R3 and R4 whereas rainfall is well correlated (R>0.68) in all the regions. Lightning flashes are better correlated (R>0.57) with temperature in R1, R2 and R4 and moderately correlated in R3 (R=0.44). Rainfall in R3 is very well correlated (R=0.91) with surface temperature and there is insignificant correlation in R1 (R=0.09). There is very good positive correlation (R>0.59) between cloud cover and convective rainfall in the entire region and well negative correlation (-0.83<R<-0.61) between OLR and convective rainfall. OLR and cloud cover show little impact on lightning flashes. Lightning flashes and convective rainfall show average positive correlation (0.48<R<0.53). Aerosol concentration is the largest in region R4 and showed an increasing trend between 2007 and 2011. Lightning flashes and convective rainfall are positively correlated (0.10<R<0.58) with aerosol concentration
Hydrographical characteristics and oxygen isotopic signatures of water in a coastal environment (Mangalore) along the southeastern Arabian Sea
No full textCoastal marine environments are important links between the continents and the open ocean. The coast off Mangalore forms part of the upwelling zone along the southeastern Arabian Sea. The temperature, salinity, density, dissolved oxygen and stable oxygen isotope ratio (δ18O) of surface waters as well as those of bottom waters off coastal Mangalore were studied every month from October 2010 to May 2011. The coastal waters were stratified in October and November due to precipitation and runoff. The region was characterised by upwelled bottom waters in October, whereas the region exhibited a temperature inversion in November. The surface and bottom waters presented almost uniform properties from December until April. The coastal waters were observed to be most dense in January and May. Comparatively cold and poorly oxygenated bottom waters during the May sampling indicated the onset of upwelling along the region. δ18O of the coastal waters successfully documented the observed variations in the hydrographical characteristics of the Mangalore coast during the monthly sampling period. We also noted that the monthly variability in the properties of the coastal waters of Mangalore was related to the hydrographical characteristics of the adjacent open ocean inferred from satellite-derived surface winds, sea surface height anomaly data and sea surface temperature