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811.
The study to establish the optimum time span for distinguishing Avena ludoviciana from wheat crop based on their spectral signatures was carried out at Student’s Research Farm, Department of Agronomy during
2006–07 and 2007–08. The experimental sites during both the seasons were sandy loam in texture, with normal soil reaction
and electrical conductivity, low in organic carbon and available nitrogen and medium in available phosphorus and potassium.
The experiment was laid out in randomized block design with four replications and consisting of twelve treatments comprising
0, 10, 15, 25, 50, 75, 100, 125, 150, 200, 250 plants m−2 and a pure Avena ludoviciana plot (Tmax). The results revealed that in all the treatments irrespective of wheat and weeds, the red reflectance (%) value decreased
from 34 to 95 DAS (days after sowing) in 2006–07 and 45 DAS to 100 DAS during 2007–08, and thereafter a sharp increase was
observed in all the treatments. This trend might be due to increased chlorophyll index after 34 DAS as red reflectance was
reduced by chlorophyll absorption. Among all the treatments, Tmax (Pure Avena ludoviciana plot) had the highest red reflectance and T0 (Pure wheat plot) had a lowest value of red reflectance during both the years. The highest value of IR reflectance was obtained
at 95 DAS (2006–07) and 70 DAS (2007–08) in all the treatments. IR reflectance of wheat crop ranged between 24.61 and 61.21
per cent during 2006–07 and 27.33 and 67.3 per cent during 2007–08. However, IR reflectance values declined after 95 DAS and
70 DAS up to harvesting during 2006–07 and 2007–08. This lower reflectance may have been due to the onset of senescence. The
highest RR and NDVI values were recorded under pure wheat treatment and minimum under pure weed plots. This may be due to
dark green colour and better vigor of the wheat as compared to Avena ludoviciana. It was observed that by using RR and NDVI, pure wheat can be distinguished from pure populations of Avena ludoviciana after 34 DAS and different levels of weed populations can be discriminated amongst themselves from 68 DAS up to 107 DAS during
both the years of investigation. 相似文献
812.
Integrating terrain and vegetation indices for identifying potential soil erosion risk area 总被引:1,自引:0,他引:1
Arabinda Sharma 《地球空间信息科学学报》2010,13(3):201-209
The present paper offers an innovative method to monitor the change in soil erosion potential by integrating terrain and vegetation indices derived from remote sensing data. Three terrain indices namely, topographic wetness index (TWI), stream power index (SPI) and slope length factor (LS), were derived from the digital elevation model. Normalized vegetation index (NDVI) was derived for the year 1988 and 2004 using remote sensing images. K-mean clustering was performed on staked indices to categorize the study area into four soil erosion potential classes. The validation of derived erosion potential map using USLE model showed a good agreement. Results indicated that there was a significant change in the erosion potential of the watershed and a gradual shifting of lower erosion potential class to next higher erosion potential class over the study period. 相似文献
813.
Elizabeth J. Petrie Matt A. King Philip Moore David A. Lavallée 《Journal of Geodesy》2010,84(8):491-499
This study provides a first attempt at quantifying potential signal bending effects on the GPS reference frame, coordinates
and zenith tropospheric delays (ZTDs). To do this, we homogeneously reanalysed data from a global network of GPS sites spanning
14 years (1995.0–2009.0). Satellite, Earth orientation, tropospheric and ground station coordinate parameters were all estimated.
We tested the effect of geometric bending and dTEC bending corrections, which were modelled at the observation level based,
in part, on parameters from the International Reference Ionosphere 2007 model. Combined, the two bending corrections appear
to have a minimal effect on site coordinates and ZTDs except for low latitude sites. Considering five days (DOY 301–305, 28
October–1 November 2001) near ionospheric maximum in detail, they affect mean ZTDs by up to ~1.7 mm at low latitudes, reducing
to negligible levels at high latitudes. Examining the effect on coordinates in terms of power-spectra revealed the difference
to be almost entirely white noise, with noise amplitude ranging from 0.3 mm (high latitudes) to 2.4 mm (low latitudes). The
limited effect on station coordinates is probably due to the similarity in the elevation dependence of the bending term with
that of tropospheric mapping functions. The smoothed z-translation from the GPS reference frame to ITRF2005 changes by less than 2 mm, though the effect combines positively with
that from the second order ionospheric refractive index term. We conclude that, at the present time, and for most practical
purposes, the geometric and dTEC bending corrections are probably negligible at current GPS/reference frame precisions. 相似文献
814.
Nowadays, NASA is producing several terabytes Moderate Resolution Imaging Spectroradiometer (MODIS) data everyday; how to find the data with criteria, such as specific times, locations, and scales using an international standard becomes more and more important. In this paper, a service-oriented architecture for use of the integration Earth Observation System Clearing-HOuse (ECHO) with the Open Geospatial Consortium (OGC) Catalogue Service—Web profile (CSW) is put forward. The architecture consists of three roles: a service requester (the user), a service provider (the ECHO metadata server), and a service broker (the GeoNetwork CSW and MODIS registry service middleware). The core component-MODIS registry service middleware includes three components: metadata fetcher, metadata transformer, and metadata register. The metadata fetcher is used to fetch metadata from ECHO metadata server; the metadata transformer is responsible for transform metadata from one form to another; the metadata register is in charge of registering ISO19139-based metadata to CSW. A prototype system is designed and implemented by using the service middleware technology and a standard interface and protocol. The feasibility and the response time of registry and retrieval of MODIS data are evaluated by means of a realistic LPDAAC_ECS MODIS data center. The implementation of this prototype system and the experiment show that the architecture and method is feasible and effective. 相似文献
815.
Approaches for delineating landslide hazard areas using different training sites in an advanced artificial neural network model 总被引:10,自引:0,他引:10
The current paper presents landslide hazard analysis around the Cameron area, Malaysia, using advanced artificial neural networks with the help of Geographic Information System (GIS) and remote sensing techniques. Landslide locations were determined in the study area by interpretation of aerial photographs and from field investigations. Topographical and geological data as well as satellite images were collected, processed, and constructed into a spatial database using GIS and image processing. Ten factors were selected for landslide hazard including: 1) factors related to topography as slope, aspect, and curvature; 2) factors related to geology as lithology and distance from lineament; 3) factors related to drainage as distance from drainage; and 4) factors extracted from TM satellite images as land cover and the vegetation index value. An advanced artificial neural network model has been used to analyze these factors in order to establish the landslide hazard map. The back-propagation training method has been used for the selection of the five different random training sites in order to calculate the factor’s weight and then the landslide hazard indices were computed for each of the five hazard maps. Finally, the landslide hazard maps (five cases) were prepared using GIS tools. Results of the landslides hazard maps have been verified using landslide test locations that were not used during the training phase of the neural network. Our findings of verification results show an accuracy of 69%, 75%, 70%, 83% and 86% for training sites 1, 2, 3, 4 and 5 respectively. GIS data was used to efficiently analyze the large volume of data, and the artificial neural network proved to be an effective tool for landslide hazard analysis. The verification results showed sufficient agreement between the presumptive hazard map and the existing data on landslide areas. 相似文献
816.
Integer least-squares theory for the GNSS compass 总被引:5,自引:2,他引:5
P. J. G. Teunissen 《Journal of Geodesy》2010,84(7):433-447
Global navigation satellite system (GNSS) carrier phase integer ambiguity resolution is the key to high-precision positioning
and attitude determination. In this contribution, we develop new integer least-squares (ILS) theory for the GNSS compass model,
together with efficient integer search strategies. It extends current unconstrained ILS theory to the nonlinearly constrained
case, an extension that is particularly suited for precise attitude determination. As opposed to current practice, our method
does proper justice to the a priori given information. The nonlinear baseline constraint is fully integrated into the ambiguity
objective function, thereby receiving a proper weighting in its minimization and providing guidance for the integer search.
Different search strategies are developed to compute exact and approximate solutions of the nonlinear constrained ILS problem.
Their applicability depends on the strength of the GNSS model and on the length of the baseline. Two of the presented search
strategies, a global and a local one, are based on the use of an ellipsoidal search space. This has the advantage that standard
methods can be applied. The global ellipsoidal search strategy is applicable to GNSS models of sufficient strength, while
the local ellipsoidal search strategy is applicable to models for which the baseline lengths are not too small. We also develop
search strategies for the most challenging case, namely when the curvature of the non-ellipsoidal ambiguity search space needs
to be taken into account. Two such strategies are presented, an approximate one and a rigorous, somewhat more complex, one.
The approximate one is applicable when the fixed baseline variance matrix is close to diagonal. Both methods make use of a
search and shrink strategy. The rigorous solution is efficiently obtained by means of a search and shrink strategy that uses
non-quadratic, but easy-to-evaluate, bounding functions of the ambiguity objective function. The theory presented is generally
valid and it is not restricted to any particular GNSS or combination of GNSSs. Its general applicability also applies to the
measurement scenarios (e.g. single-epoch vs. multi-epoch, or single-frequency vs. multi-frequency). In particular it is applicable
to the most challenging case of unaided, single frequency, single epoch GNSS attitude determination. The success rate performance
of the different methods is also illustrated. 相似文献
817.
HWANG Chenway 《地球空间信息科学学报》2010,13(2):144-149
The quality of altimeter data and ocean tide model is critical to the recovery of coastal gravity anomalies. In this contribution, three retracking methods (threshold, improved threshold and Beta-5) are investigated with the aim of improving the altimeter data over a shallow water area. Comparison indicates that the improved threshold is the best retracking method over China Sea. Two ocean tide models, NAO99b and CSR4.0, are analyzed. Results show that different tide models used in the processing of altimeter data may result in differences more than 10 mGal in recovered coastal gravity anomalies. Also, NAO99b is more suitable than CSR4.0 over the shallow water area of China Sea. Finally, gravity anomalies over China Sea are calculated from retracked Geosat/GM and ERS-1/GM data by least squares collocation. Comparison with shipborne gravimetry data demonstrates that gravity anomalies from retracked data are significantly superior to those from non-retracked data. Our results have the same order as the other two altimeter-derived gravity models: Sandwell&Smith(V16) and DNSC08. 相似文献
818.
Mohammad Sharifikia 《Journal of the Indian Society of Remote Sensing》2010,38(4):708-716
Earthquakes cause huge loss of lives and infrastructure every year in Iran. Many settlement areas (urban & rural) as well
as Tehran, the capital city of Iran are located in the hazardous area. This research deals with the earthquake risk assessment
and mapping based on recent remote sensing information on a GIS platform. The study area is part of Central Alborz in southern
Caspian Sea and north of capital city of Tehran called Marzanabad area. It is a potentially high-risk zone as several earthquakes
have occurred in the past. The study’s main objective is to develop an Earthquake Risk Map at the scale of 1:25,000 to identify
high-risk zone and vulnerability areas to the settlements and infrastructure of area. Digital lineaments wear extraction and
analysis for identification the faults using several RADAR and optical images with spatial analysis techniques. The probable
faults were detected by superimposition of the lithological and geomorphologic features and their variance over the lineaments
in a GIS environment. This research work involved fault identification on the remote sensed dataset as well as field studies
and the risky areas were classified in the vicinity of the faults by applying different buffer with specifying distance of
the source/site of risk to fault location. Statistical analysis of Earthquake Risk Map (ERM) by GIS indicated that 32% of
the total area with about 66% of settlements and 52% of population is located in strongly high-risk and high-risk zone. Moderately
low risk and low risk zones cover 38.67% of total area, which is free of settlements as well as population. The Earthquake
map elaborated in this research work will be a useful tool for disaster management as well as urban and regional planning
of future activities in the area. 相似文献
819.
An Introduction to MODISI and SCMOD Methods for Correction of the MODIS Snow Assessment Algorithm 总被引:1,自引:0,他引:1
Mohammad Reza Mobasheri Hossein Shafizadeh Moghadam Siavosh Shayan 《Journal of the Indian Society of Remote Sensing》2010,38(4):674-685
Detection, monitoring and precise assessment of the snow covered regions is an important issue. Snow cover area and consequently
the amount of runoff generated from snowmelt have a significant effect on water supply management. To precisely detect and
monitor the snow covered area we need satellite images with suitable spatial and temporal resolutions where we usually lose
one for the other. In this study, products of two sensors MODIS and ASTER both on board of TERRA platform having low and high
spatial resolution respectively were used. The objective of the study was to modify the snow products of MODIS by using simultaneous
images of ASTER. For this, MODIS snow index image with high temporal resolution were compared with that of ASTER, using regression
and correlation analysis. To improve NDSI index two methods were developed. The first method generated from direct comparison
of ASTER averaged NDSI with those of MODIS (MODISI). The second method generated by dividing MODIS NDSI index into 10 codes
according to their percentage of surface cover and then compared the results with the difference between ASTER averaged and
MODIS snow indices (SCMOD). Both methods were tested against some 16 MODIS pixels. It is found that the precision of the MODISI
method was more than 96%. This for SCMOD was about 98%. The RMSE of both methods were as good as 0.02. 相似文献
820.
Michael Huettner Annette Freibauer Constanze Haug Uwe Cantner 《Carbon balance and management》2010,5(1):2
The 'Copenhagen Accord' fails to deliver the political framework for a fair, ambitious and legally-binding international climate
agreement beyond 2012. The current climate policy regime dynamics are insufficient to reflect the realities of topical complexity,
actor coalitions, as well as financial, legal and institutional challenges in the light of extreme time constraints to avoid
'dangerous' climate change of more than 2°C. In this paper we analyze these stumbling blocks for international climate policy
and discuss alternatives in order to regain momentum for future negotiations. 相似文献