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1.
Reservoir sedimentation is the gradual accumulation of incoming sediments from upstream catchment leading to the reduction in useful storage capacity of the reservoir. Quantifying the reservoir sedimentation rate is essential for better water resources management. Conventional techniques such as hydrographic survey have limitations including time-consuming, cumbersome and costly. On the contrary, the availability of high resolution (both spatial and temporal) in public domain overcomes all these constraints. This study assessed Jayakwadi reservoir sedimentation using Landsat 8 OLI satellite data combined with ancillary data. Multi-date remotely sensed data were used to produce the water spread area of the reservoir, which was applied to compute the sedimentation rate. The revised live storage capacity of the reservoir between maximum and minimum levels observed under the period of analysis (2015–2017) was assessed utilizing the trapezoidal formula. The revised live storage capacity is assessed as 1942.258 against the designed capacity of 2170.935 Mm3 at full reservoir level. The total loss of reservoir capacity due to the sediment deposition during the period of 41 years (1975–2017) was estimated as 228.677 Mm3 (10.53%) which provided the average sedimentation rate of 5.58 Mm3 year1. As this technique also provides the capacity of the reservoir at the different elevation on the date of the satellite pass, the revised elevation–capacity curve was also developed. The sedimentation analysis usually provides the volume of sediment deposited and rate of the deposition. However, the interest of the reservoir authorities and water resources planner’s lies in sub-watershed-wise sediment yield, and the critical sub-watersheds upstream reservoir requires conservation, etc. Therefore, in the present study, Soil and Water Assessment Tool (SWAT) was used for the estimation of sediment yield of the reservoir. The average annual sediment yield obtained from the SWAT model using 36 years of data (1979–2014) was 13.144 Mm3 year?1 with the density of the soil (loamy and clay) of 1.44 ton m?3. The findings revealed that the rate of sedimentation obtained from the remote sensing-based methods is in agreement with the results of the hydrographic survey.  相似文献   

2.
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   

3.
Reservoir water levels extracted from SARAL/AltiKa GDR data for the period 2013–2014 and water spread areas delineated from Resourcesat P6-AWiFS sensor and RISAT 1 microwave data corresponding to SARAL/AltiKa cycles were used for assessment of reservoir capacity in the Mayurakshi reservoir, Jharkhand state, India. It was found that the reservoir capacity based on the SARAL is around 474.62 Mm3 in comparison to in situ based estimate i.e. around 486.6 Mm3, indicating variation of <3%. Further, comparison of these estimates computed using SARAL and in situ with original reservoir capacity (547.59 Mm3) indicated loss of reservoir capacity is around 13.33 and 11.14%, respectively, within a span of 59 years. The hydrographic survey in the year 1999–2000 also proved that the storage capacity has reduced from 547.6 Mm3 in 1955 to 474.8 Mm3 indicating loss of nearly 13.3 % of total live capacity over period of 45 years.  相似文献   

4.
One of the most prominent geomorphological features in the Western Desert of Egypt is the occurrence of the Qattara Depression (20,800 km2 or 2% of Egypt’s area), which has the deepest point in Africa. Topographic analysis of the depression was carried out using fine resolution digital elevation models acquired from the Advanced Spaceborne Thermal Emission and Reflection Radiometer-Global Digital Elevation Model (ASTER-GDEM) in order to assess the capacity of the depression. Results showed that the lower point in the depression occurs at ?136 m and its capacity at the sea level is 1340 billion m3, which equals 10 times the live storage capacity of the Lake Nasser behind the Aswan High Dam. Although the depression has the aptitude to be a reservoir for any augmentation in the sea level, detailed environmental impact assessment studies should be implemented to address geologic, climatic, biologic as well as socio-economic impacts.  相似文献   

5.
The problem of “global height datum unification” is solved in the gravity potential space based on: (1) high-resolution local gravity field modeling, (2) geocentric coordinates of the reference benchmark, and (3) a known value of the geoid’s potential. The high-resolution local gravity field model is derived based on a solution of the fixed-free two-boundary-value problem of the Earth’s gravity field using (a) potential difference values (from precise leveling), (b) modulus of the gravity vector (from gravimetry), (c) astronomical longitude and latitude (from geodetic astronomy and/or combination of (GNSS) Global Navigation Satellite System observations with total station measurements), (d) and satellite altimetry. Knowing the height of the reference benchmark in the national height system and its geocentric GNSS coordinates, and using the derived high-resolution local gravity field model, the gravity potential value of the zero point of the height system is computed. The difference between the derived gravity potential value of the zero point of the height system and the geoid’s potential value is computed. This potential difference gives the offset of the zero point of the height system from geoid in the “potential space”, which is transferred into “geometry space” using the transformation formula derived in this paper. The method was applied to the computation of the offset of the zero point of the Iranian height datum from the geoid’s potential value W 0=62636855.8 m2/s2. According to the geometry space computations, the height datum of Iran is 0.09 m below the geoid.  相似文献   

6.
Due to the super rotation of the Earth＇s inner core, the tilted figure axis of the inner core would progress with respect to the mantle and thus cause the variation of the Earth＇s external gravity field. This paper improves the present model of the gravity field variation caused by the inner core super rotation. Under the assumption that the inner core is a stratifying ellipsoid whose density function is fitted out from PREM and the super rotation rate is 0.27-0.53°/yr, calculations show that the global temporal variations on the Earth＇s surface have a maximum value of about 0.79-1.54×10^3 pGal and a global average intensity of about 0.45-0.89×10^ 3 μGal in the whole year of 2007, which is beyond the accuracy of the present gravimetry and even the super conducting gravimeter data. However, both the gravity variations at Beijing and Wuhan vary like sine variables with maximal variations around 0.33 pGal and 0.29 pGal, respectively, in one cycle. Thus, continuous gravity measurements for one or two decades might be able to detect the differential motion of the inner core.  相似文献   

7.
    
Résumé L’Institut Géographique National a fait réaliser par les Etablissements Brillié des chronographes imprimants au 1/100e de seconde pour répondre aux besoins particuliers des missions exécutant des travaux d’astronomie de position dans les territoires d’Outre-Mer. Ces appareils permettent d’une part l’enregistrement des signaux horaires re?us par radio et, par suile, la détermination de l’état du chronomètre de synchronisation, d’autre part, l’enregistrement des observations astronomiques. Le chronographe imprimant comprend essentiellement un moteur à courant continu, faisant un tour par seconde, qui entraìne un commutateur tournant, destiné à assurer sa synchronisation par un chronomètre de marine Leroy à contacts électriques. Le moteur commande un groupe de molettes gravées contr?lées par un cadran témoin, qui permet de mettre à l’heure le chronographe imprimant par rapport au chronomètre de marine. A chaque enregistrement deux opéralions s’effectuent sous l’action de deux électro-aimants agissant simultanément: lo Des marteaux viennent presser contre les molettes un ruban encreur et la bande de papier, provoquant ainsi l’impression. 2o La bande de papier avance d’environ 15 m/m., permettant de voir la frappe inserite et d’en effectuer une nouvelle. La synchronisation est assurée toutes les 1/2 secondes. Un amplificateur spécial, indépendant du chronographe, sert à la fois d’organe de liaison entre le récepteur radio et le chronographe et de tableau de commande pour celui-ci. L’appareil a été mis sous carter étanche. L’alimentation est assurée par deux batteries d’accumulateurs. L’ensemble du matériel peut être facilement transporté en campagne. De nombreuses mesures ont été faites, soit au laboratoire, soit au cours de missions sur le terrain: l’erreur moyenne accidentelle sur l’enregistrement d’un top est de ±0s,015 environ. Communication présentée à l’Assemblée Générale de la Société Chronométrique de France (23 avril 1949). Cette étude a été publiée également dans lesAnnales fran?aises de Chronométrie. t. III, 3e trimestre 1949 (p. 295–311).  相似文献   

8.
 A methodology for precise determination of the fundamental geodetic parameter w 0, the potential value of the Gauss–Listing geoid, as well as its time derivative 0, is presented. The method is based on: (1) ellipsoidal harmonic expansion of the external gravitational field of the Earth to degree/order 360/360 (130 321 coefficients; http://www.uni-stuttgard.de/gi/research/ index.html projects) with respect to the International Reference Ellipsoid WGD2000, at the GPS positioned stations; and (2) ellipsoidal free-air gravity reduction of degree/order 360/360, based on orthometric heights of the GPS-positioned stations. The method has been numerically tested for the data of three GPS campaigns of the Baltic Sea Level project (epochs 1990.8,1993.4 and 1997.4). New w 0 and 0 values (w 0=62 636 855.75 ± 0.21 m2/s2, 0=−0.0099±0.00079 m2/s2 per year, w 0/&γmacr;=6 379 781.502 m,0/&γmacr;=1.0 mm/year, and &γmacr;= −9.81802523 m2/s2) for the test region (Baltic Sea) were obtained. As by-products of the main study, the following were also determined: (1) the high-resolution sea surface topography map for the Baltic Sea; (2) the most accurate regional geoid amongst four different regional Gauss–Listing geoids currently proposed for the Baltic Sea; and (3) the difference between the national height datums of countries around the Baltic Sea. Received: 14 August 2000 / Accepted: 19 June 2001  相似文献   

9.
Based on the gravity field models EGM96 and EIGEN-GL04C, the Earth＇s time-dependent principal moments of inertia A, B, C are obtained, and the variable rotation of the Earth is determined. Numerical results show that A, B, and C have increasing tendencies; the tilt of the rotation axis increases 2.1×10^ 8 mas/yr; the third component of the rotational angular velocity, ω3 , has a decrease of 1.0×10^ 22 rad/s^2, which is around 23% of the present observed value. Studies show in detail that both 0 and ω3 experience complex fluctuations at various time scales due to the variations of A, B and C.  相似文献   

10.
    
Résumé Une allusion faite récemment dans ces colonnes parM. Wolf (1) à certains de mes écrits de 1948 sur les tables de corrélatifs angulaires pour la compensation des réseaux géodésiques (Boltz, Friedrich, Jenne, Marcantoni), in’incite à reprendre aujourd’hui la parole sur ce sujet pour quelques remarques suggérées par l’expérience acquise sur ces auxiliaires mathématiques intéressants. Les remarques devant avoir un caractère surtout pratique, il m’incombe auparavant de saluer comme ils le méritent les nouveaux et importants travaux donnés sur ce sujet parJenne (2), et qui élargissent encore d’une manière intéressante le domaine d’emploi des premières tables qu’on lui doit. M. Wolf,Bulletin Géodésique, no 6, décembre 1952.  相似文献   

11.
Locally computed statistics of image texture and a case-based reasoning (CBR) system were evaluated for mapping of forest attributes. Cluster analysis was preferred to regression models, as a pre-selection method of features. The best stand-based accuracy using satellite sensor images was 74.64 m−3 ha−1 (36%) RMSE for stand volume, 1.98 m−3 ha−1 a−1 (49%) for annual increase in stand volume, where κ = 0.23 for stand growth classes and κ = 0.41 for dominant tree species in stands. The top pixel-based accuracy using orthophotos was 76.54 m−3 ha−1 (41%) RMSE for stand volume, 1.87 m−3 ha−1 a−1 (44%) for annual increase in stand volume, where κ = 0.24 for stand growth classes and κ = 0.38 for dominant tree species in stands. Mean saturation in 30 m radius was the most useful feature when orthophotos were used, and standard deviation of Landsat ETM 6.2 values in 80 m radius was the best when satellite sensor images were used. The most valuable feature components (radii, channels and local statistics) for orthophotos were: 30 m kernel radius, lightness and the mean of pixel values; for satellite sensor images: 80 m kernel radius, near-infrared channel (ETM 4) and the mean of pixel values. Locally computed statistics.  相似文献   

12.
The method of Bjerhammar is studied in the continuous case for a sphere. By varying the kernel function, different types of unknowns (u*) are obtained at the internal sphere (the Bjerhammar sphere). It is shown that a necessary condition for the existence of u* is that the degree variances (σ n 2 ) of the observations are of an order less than n−2. According to Kaula’s rule this condition is not satisfied for the earth’s gravity anomaly field (σ n 2 =n−1) but well for the geopotential (σ n 2 =n−3).  相似文献   

13.
Sentinel-2数据的冬小麦地上干生物量估算及评价   总被引：3，自引：0，他引：3  
郑阳  吴炳方  张淼 《遥感学报》2017,21(2):318-328
作物生物量快速精确的监测对于农业资源的合理利用与农田的精准管理具有重要意义。近年来,遥感技术因其独特的优势已被广泛用于作物生物量的估算中。本文主要针对不同宽波段植被指数在冬小麦生物量(文中的生物量均是指地上干生物量)估算方面的表现进行探索。首先利用欧洲空间局最新的Sentinel-2A卫星数据提取出17种常见的植被指数,之后分别构建其与相应时期内采集的冬小麦地上生物量间的最优估算模型,通过分析两者间的相关性与敏感性,获取适宜进行生物量估算的指数。最后,绘制了研究区的生物量空间分布图。结果表明,所选的植被指数均与生物量显著相关。其中,红边叶绿素指数(CI_(re))与生物量的估算精度最高(决定性系数R~2为0.83;均方根误差RMSE为180.29 g·m~(–2))。虽然相关性较高,但部分指数,如归一化差值植被指数(NDVI)等在生物量较高时会出现饱和现象,从而导致生物量的低估。而加入红边波段的指数不仅能够延缓指数的饱和趋势,而且能够提高反演精度。此外,通过敏感性分析发现,归一化差值指数和比值指数分别在作物生长的早期和中后期对生物量的变化保持较高的敏感性。由于红边比值指数(SR_(re))和MERIS叶绿素敏感指数(MTCI)在冬小麦全生长季内一直对生物量的变化保持高灵敏性,二者是生物量估算中最为稳定的指数。  相似文献   

14.
Net Primary Productivity (NPP) is a significant biophysical vegetation variable to understand the spatio-temporal distribution of carbon and source-sink nature of the ecosystem. This study was carried out in a forest plantation area and aimed to (i) estimate the spatio-temporal patterns of NPP during 2009 and 2010 using Carnegie-Ames-Stanford Approach [CASA] model and (ii) study the effects of climate variables on the NPP using generalized linear modelling (GLM) approach. The total annual NPP varied from 157.21 to 1030.89 gC m?2 yr?1 for the year 2009 and from 154.36 to 1124.85 g C m?2 yr?1 for the year 2010. The annual NPP was assessed across four major plantation types, where maximum NPP gain (106 and 139 g C m?2 yr?1 ) in October was noticed in teak (Tectona grandis) and minimum (77 and 109 g C m?2 yr?1 ) in eucalyptus (Eucalyptus hybrid) during 2009 and 2010.The validation, using field-estimated NPP, showed under-estimation of modelled NPP, with maximum MAPE of 34% for eucalyptus and minimum of 13% for teak. The dominant influence of precipitation on the NPP was revealed by GLM explaining more than 20% of variation. CASA model efficiently estimated the annual NPP of plantations. The accuracy could be improved further with inclusion of higher resolution data.  相似文献   

15.

Background

To address how natural disturbance, forest harvest, and deforestation from reservoir creation affect landscape-level carbon (C) budgets, a retrospective C budget for the 8500 ha Sooke Lake Watershed (SLW) from 1911 to 2012 was developed using historical spatial inventory and disturbance data. To simulate forest C dynamics, data was input into a spatially-explicit version of the Carbon Budget Model-Canadian Forest Sector (CBM-CFS3). Transfers of terrestrial C to inland aquatic environments need to be considered to better capture the watershed scale C balance. Using dissolved organic C (DOC) and stream flow measurements from three SLW catchments, DOC load into the reservoir was derived for a 17-year period. C stocks and stock changes between a baseline and two alternative management scenarios were compared to understand the relative impact of successive reservoir expansions and sustained harvest activity over the 100-year period.

Results

Dissolved organic C flux for the three catchments ranged from 0.017 to 0.057 Mg C ha?1 year?1. Constraining CBM-CFS3 to observed DOC loads required parameterization of humified soil C losses of 2.5, 5.5, and 6.5%. Scaled to the watershed and assuming none of the exported terrestrial DOC was respired to CO2, we hypothesize that over 100 years up to 30,657 Mg C may have been available for sequestration in sediment. By 2012, deforestation due to reservoir creation/expansion resulted in the watershed forest lands sequestering 14 Mg C ha?1 less than without reservoir expansion. Sustained harvest activity had a substantially greater impact, reducing forest C stores by 93 Mg C ha?1 by 2012. However approximately half of the C exported as merchantable wood during logging (~176,000 Mg C) may remain in harvested wood products, reducing the cumulative impact of forestry activity from 93 to 71 Mg C ha?1.

Conclusions

Dissolved organic C flux from temperate forest ecosystems is a small but persistent C flux which may have long term implications for C storage in inland aquatic systems. This is a first step integrating fluvial transport of C into a forest carbon model by parameterizing DOC flux from soil C pools. While deforestation related to successive reservoir expansions did impact the watershed-scale C budget, over multi-decadal time periods, sustained harvest activity was more influential.
  相似文献   

16.
Mapping of oceanic productive zones through an optical sensor on board a satellite requires a detailed knowledge about the interaction of solar flux with the atmosphere and water column. Hence the radiative transfer on February 14, 2002 over estuaries of Goa has been examined through a couple radiative transfer model (CRTM). This has been carried out in the context of an optical sensor when it looks down at nadir. The forcing of extraterrestrial solar irradiance with atmosphere results in its absorption and scattering due to aerosol particles and gaseous constituents and rayleigh particles. The optical spectrum has been subjected to atmospheric forcing and radiation has been calculated for every 1 nm. Special reference is given to two wavelengths (443 and 510 nm), which are important for ocean optics. The atmospheric components pertaining to these wavelengths are 0.04193 w/m2/nm/sr and 0.0225 w/m2/nm/sr (rayleigh) and 0.0121 w/m2/nm/sr and 0.015 w/m2/nm/sr (aerosol). Within the optical frame work (400 –700 nm), the effect of aerosol overrides that of rayleigh from 545 nm onwards. The specular reflectance at the sea surface contributes 1.725 x l0-12 w/m2/nm/sr and 1.947x 10-12 w/m2/nm/sr while the respective signature from water column is 0.418x 10-3w/m2/nm/sr and 0.536x 10-3 w/m2/nm/sr. The simulated water signature has been compared with radiances measured by a radiometer (Satlantic radiometer). The correlation (R2) is found to be around 0.97. The sensitivity analysis further reveals the respective wavelengths of the optical spectrum affected by atmospheric and oceanic constituents. Moreover, the effect of change in solar zenith angle on water signature has also been carried out. This could be applied to invert satellite data so as to retrieve coastal water constituents and productivity.  相似文献   

17.
A study aimed at generating wheat yield maps of farmer’s fields by using remote sensing (RS) inputs was undertaken during the rabi season of 1998-99 in six villages of Alipur Block of Delhi State. RS derived leaf area index (LAI) were linked to wheat simulation model WTGROWS by adopting a strategy christened “Modified Corrective Approach”. This essentially uses an empirical relation of grain yield and LAI, which was derived from WTGROWS simulation model by running model for a combination of input resources, management practices and soil types occurring in the area. This biometric relationship was applied to all the wheat fields of the study area for which the LAI was derived from single acquisition of IRS LISS-III data (Jan 27, 99). The LAI-NDVI relation adopted was logarithmic in nature (R2=0.83) and was based on ground measurements of LAI in farmer’s fields in the same area. A comparison of predicted grain yield by the modified corrective approach and actual observed yield for the 22 farmer’s fields showed high correlation coefficient of 0.8 and a root mean square error (RMSE) of 597 kg ha-1 which was 17% of the observed mean yield. Thus linking of RS information and crop simulation model provides an alternative for mapping and forecasting crop yield under highly variable cropping environment of Indian farms, which is a pre-requisite for implementing Precision Crop Management (PCM).  相似文献   

18.
Himalayas possess one of the largest resources of snow, ice and glaciers that act as a huge freshwater reservoir. Monitoring the glaciers is important to assess the overall reservoir health of the Himalayas. Samudra Tapu is one of the largest glaciers in Chandra basin of district Lahaul and Spiti, Himachal Pradesh. Based on the field investigations and the remote sensing techniques. features such as accumulation area, ablation area snowline/equilibrium line, moraine-dammed lakes and permanent snowfields were mapped. The glacial terminus was identified using moraine-dammed lake, as lake is located at down streamside of the terminus. The total recession of glacier during the period of 38 years (1962–2000) is about 742 m with an average rate of 19.5 m/yr. In addition, glacial extent is reduced from 73 to 65 km2 between 1962 and 2000. suggesting overall deglaciation of 11%. During field investigation. three stages of glaciation using terminal moraine were identified. These moraines were mapped by merging LISS-II1 and PAN data. At the peak of glaciation. the glacial terminus was extended 3.18 km downstream of terminus position in year 2000. Total area during peak of glaciation period has been observed to be 77.67 km2, which is 12.67 km2 higher than the present glacier extent.  相似文献   

19.
The present study aimed at quantification of sediment yield for Ahar River basin of Udaipur district in Rajasthan, India by a regional empirical model using RS and GIS techniques. The land use/land cover (LULC) map of the study area was prepared by supervised classification using satellite imagery of IRS-P6 LISS III. Overall accuracy of the prepared LULC map was 90.78%. The major portion of the study area (49%) is covered with rangeland. Slope map for the study area was developed using digital elevation model. The slope in most of the study area (40% of the total area) ranges from 1% to 4%. In addition, drainage density map of the study area was generated on micro-watershed basis. The study area is covered by a dendritic pattern of drainage which shows that rocks in the area are homogeneous and uniformly resistant to water flow. The drainage density in the study area is 1.11 km km−2. Annual sediment yield of the study area was quantified by Garde model. The mean annual runoff and sediment yield for the area was 37.58 million m3 and 8,760 m3/year, respectively. Finally, appropriate sites for construction of soil conservation measures are suggested using Boolean logic analysis method on combined slope and drainage maps.  相似文献   

20.
Seasonal snow melt in the Wind River Range, Wyoming, has been ending earlier over the last several decades leaving the region to rely more on supplemental melt water from mountain glaciers. This leads to the necessity of understanding recent glacial changes. This study uses elevation data from 1966, 2006 and 2011 to calculate surface elevation and volume changes that have occurred on Continental Glacier. Results indicate a mean volume change of ?0.034 ± 0.02 km3 and surface elevation change of ?0.36 ± 0.19 m y?1 between 1966 and 2006. Detailed spatial analysis shows that the glacier is divided into two sections which are thinning at different rates (lower section: ?0.06±0.19 m y?1; upper section: ?0.51 ± 0.19 m y?1). The upper section has experienced 97% of the thinning (or 742.5 × 103 m3 of melt water equivalent per year) and increased its rate since 2006 by 27.5%.  相似文献   

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