Showing papers in "Remote Sensing in 2003"
TL;DR: In this article, a prototype in-situ sensorweb was deployed in the Roseau River Sub-Basin of the Red River Watershed in Manitoba, Canada in September 2002 and remained there throughout the flood season until the end of June 2003.
Abstract: This paper describes work towards building an integrated Earth sensing capability and focuses on the demonstration of a prototype in-situ sensorweb in remote operation in support of flood forecasting. A five-node sensorweb was deployed in the Roseau River Sub-Basin of the Red River Watershed in Manitoba, Canada in September 2002 and remained there throughout the flood season until the end of June 2003. The sensorweb operated autonomously, with soil moisture
measurements and standard meteorological parameters accessed remotely via land line and/or satellite from the Integrated Earth Sensing Workstation (IESW) at the Canada Centre for Remote Sensing (CCRS) in Ottawa. Independent soil moisture data were acquired from actual grab samples and field-portable sensors on the days of RADARSAT and
Envisat Synthetic Aperture Radar (SAR) data acquisitions. The in-situ data were used to help generate spatial soil moisture estimates from the remotely sensed SAR data for use in a hydrological model for flood forecasting.
11 citations
Journal Article•
TL;DR: In this article, the authors used adaptive optics techniques to correct wave front aberrations caused by atmospheric turbulence and enable near-diffraction-limited performance of the receiving telescope, which facilitates spatial filtering, and allows the receiver field-of-view and hence the noise from the sky background to be reduced.
Abstract: The deep space optical communications subsystem offers a higher bandwidth communications link in smaller size, lower mass, and lower power consumption subsystem than does RF. To demonstrate the benefit of this technology to deep space communications NASA plans to launch an optical telecommunications package on the 2009 Mars Telecommunications orbiter spacecraft. Current performance goals are 30-Mbps from opposition, and 1-Mbps near conjunction (-3 degrees Sun-Earth-Probe angle). Yet, near conjunction the background noise from the day sky will degrade the performance of the optical link. Spectral and spatial filtering and higher modulation formats can mitigate the effects of background sky. Narrowband spectral filters can result in loss of link margin, and higher modulation formats require higher transmitted peak powers. In contrast, spatial filtering at the receiver has the potential of being lossless while providing the required sky background rejection. Adaptive optics techniques can correct wave front aberrations caused by atmospheric turbulence and enable near-diffraction-limited performance of the receiving telescope. Such performance facilitates spatial filtering, and allows the receiver field-of-view and hence the noise from the sky background to be reduced.
9 citations
TL;DR: In this paper, the authors considered the possibility to realize phase reveresal in a linear system and only with the use of phase control of the beam, where the system should include two mirrors separated by the vacuum gap of a finite size.
Abstract: It was shown that there exist two sources of errors in an adaptive optics system. The first source appears due to limitations induced by the elements of the system such as a Shack Hartmann sensor and deformable mirror. The second associated with the violation of the optical reciprocity principle in algorithm of phase conjugation, namely, with substitute of beacon amplitude distribution by distribution of a Gaussian beam generated by a laser. Absolute correction of turbulent aberration is possible only in case of strict maintenance of a principle, i.e. in case of phase reversal. In the paper the possibility is considered to realize phase reveresal in a linear system and only with the use of phase control of the beam. The system should include two mirrors separated by the vacuum gap of a finite size. Estimations were obtained by correction efficiency on the base of phase conjugation and with the use of two mirror adaptive system.
2 citations
TL;DR: In this article, a two-wavelength elastic lidar was used to obtain local information on the LiDAR ratio which can be used to improve lidar profiling in inhomogeneous atmospheres and show that a key feature of any scheme is the monotonic dependance between the optical data ratio and the distribution parameter.
Abstract: Multiwavelength elastic lidar is often used to probe the aerosol profiles of the atmosphere. Normally, the atmosphere is considered homogeneous and an a-priori aerosol ratio is given for each wavelength channel which is then processed independently. However, it is clear that the multiwavelength retrieved backscatter profiles should contain information that can be used to estimate particle size distribution which may provide a new estimate to range dependant aerosol ratio profiles which can be repeated until convergence. In this paper, we illustrate the basic idea of using multiwavelength data using a two wavelength lidar to obtain local information on the lidar ratio which can be used to improve lidar profiling in inhomogeneous atmospheres and show that a key feature of any scheme is the monotonic dependance between the optical data ratio and the distribution parameter. In addition, we extend the approach to a prototypical Nd:YAG three wavelength (355, 532, 1064nm) lidar arrangement and show that while an iterative lidar procedure can be used to extract range dependant profiles, imprecision in the inversion procedure as well as error propagation of the lidar back integration can hamper convergence.