排序方式： 共有43条查询结果，搜索用时 0 毫秒
41.
Olivier Merlin Jeffrey P. Walker Jetse D. Kalma Edward J. Kim Jorg Hacker Rocco Panciera Rodger Young Gregory Summerell John Hornbuckle Mohsin Hafeez Thomas Jackson 《Advances in water resources》2008
The National Airborne Field Experiment 2006 (NAFE’06) was conducted during a three week period of November 2006 in the Murrumbidgee River catchment, located in southeastern Australia. One objective of NAFE’06 was to explore the suitability of the area for SMOS (Soil Moisture and Ocean Salinity) calibration/validation and develop downscaling and assimilation techniques for when SMOS does come on line. Airborne L-band brightness temperature was mapped at 1 km resolution 11 times (every 1–3 days) over a 40 by 55 km area in the Yanco region and 3 times over a 40 by 50 km area that includes Kyeamba Creek catchment. Moreover, multi-resolution, multi-angle and multi-spectral airborne data including surface temperature, surface reflectance (green, read and near infrared), lidar data and aerial photos were acquired over selected areas to develop downscaling algorithms and test multi-angle and multi-spectral retrieval approaches. The near-surface soil moisture was measured extensively on the ground in eight sampling areas concurrently with aircraft flights, and the soil moisture profile was continuously monitored at 41 sites. Preliminary analyses indicate that (i) the uncertainty of a single ground measurement was typically less than 5% vol. (ii) the spatial variability of ground measurements at 1 km resolution was up to 10% vol. and (iii) the validation of 1 km resolution L-band data is facilitated by selecting pixels with a spatial soil moisture variability lower than the point-scale uncertainty. The sensitivity of passive microwave and thermal data is also compared at 1 km resolution to illustrate the multi-spectral synergy for soil moisture monitoring at improved accuracy and resolution. The data described in this paper are available at www.nafe.unimelb.edu.au. 相似文献
42.
Ibrahim Zia Hina Zafar Muhammad I. Shahzad Mohsin Meraj Jamil H. Kazmi 《中国海洋大学学报(英文版)》2017,16(6):1055-1060
Indus Deltaic Region (IDR) in Pakistan is an erosion vulnerable coast due to the high deep water wave energy. Livelihood of millions of people depends on the fisheries and mangrove forests in IDR. IDR consists of many creeks where Daboo is a major creek located at southeast of the largest city of Pakistan, Karachi. Unfortunately, there has been no detailed study to analyze the damages of sea water intrusion at a large temporal and spatial scale. Therefore, this study is designed to estimate the effects of sea water inundation based on changing sea water surface salinity and sea surface temperature (SST). Sea surface salinity and SST data from two different surveys in Daboo creek during 1986 and 2010 are analyzed to estimate the damages and extent of sea water intrusion. Mean salinity has increased 33.33% whereas mean SST decreased 13.79% from 1987 to 2010. Spatio-temporal analysis of creek area using LANDSAT 5 Thematic mapper (TM) data for the years 1987 and 2010 shows significant amount of erosion at macro scale. Creek area has increased approximately 9.93% (260.86 m2 per year) which is roughly equal to 60 extensive sized shrimp farms. Further Land Use Land Cover (LULC) analyses for years 2001 and 2014 using LANDSAT 7 Enhanced Thematic Mapper Plus (ETM+) has indicated 42.3% decrease in cultivated land. Wet mud flats have spread out at the inner mouth of creek with enormous increase of 123.3%. Significant sea water intrusion has increased the area of barren land by 37.9%. This also resulted in overall decrease of 6.7% in area covered by mangroves. Therefore, this study recorded a significant evidence of sea water intrusion in IDR that has caused serious damages to community living in the area, economical losses. Additionally, it has also changed the environment by reducing creek biological productivity as reported by earlier studies over other regions of the world. 相似文献
43.
Much of the research into multipath detection and mitigation has not considered the carrier phase delay between the line of
sight (LOS) and reflected signals. A new variable referred to as early late phase (ELP) has recently been proposed to exploit
this phase difference. It has been found that in a receiver tracking the L1 GPS signal, the probability of detecting multipath
is lower when the carrier phase difference between the LOS and a reflected signal is an integer multiple of π. Since the pseudorange
error caused by the multipath’s presence is the highest in this case, we propose to exploit the coexistence of another GPS
civilian signal, the L2C. We present an analysis of ELP for the L1 and L2C signals, and a combination of both, for detecting
multipath. The multipath detection performance has been compared using probabilities of false alarm and detection. An ideal
algorithm should have lower probability of false alarm and higher probability of detection. However, it has been found that
using dual-frequency ELP increases both probabilities. Thus, receiver operator characteristics (ROC) curves, and the area
under the ROC curves, have been used for effective comparison. It has been found that the L2C signal individually gives worse
performance than L1 because of its weaker signal strength. However, the combination of L1 and L2C gives the best overall performance,
and thus it can be claimed that ELP using dual-frequency receivers is a more effective approach for detecting multipath. 相似文献