Moving target imaging algorithm for SAR data

A digital processing algorithm for fine-resolution imaging of synthetic aperture radar (SAR) moving targets is described. The targets may have any translational and rotational motion components relative to the data collection platform. The algorithm requires the presence of up to three prominent points in the image of the target; the signals from these points provide estimates of the unknown target motion parameters. Phase compensation and data formatting based on these estimates eliminate motion-induced phase errors. This algorithm has been implemented on a VAX computer and used to process both simulated and real SAR data of moving targets. Results obtained using the simulated data are presented     

Distributed computation for a tree network with communicationdelays

Tree networks of communicating processors are examined with the objective of solving a computational problem in a minimal amount of time. The processors in the networks may be equipped either with or without front-end processors for communicating of loading. The determination of the optimal division of processing load is discussed for the network with and the network without front-end processors. The inclusion of solution time, the time taken for sensors to report the solution back to originator, is discussed     

A new clutter rejection method using a robust polarimetricCFAR-detector

Two methods for constructing robust polarimetric constant-false-alarm-rate (CFAR) detectors that use elements of the scattering matrix are discussed. Both methods use robust estimators to recognize outliers and exclude them from further calculations. The first method weighs each sample of the surrounding vectors, and vectors that appear to be outliers are weighted with lower values than the others. The second method uses cluster algorithms to arrange the data in different clusters; some clusters contain the outliers, and others contain observations assumed to come from the main body of the data. The detectors are intended to be used in multitarget and nonhomogeneous-clutter environments     

Next generation digital GPS receiver

The architecture and technology features of the next-generation (NGR) digital GPS (Global Positioning System) receiver manufactured by Collin are described. The project's objective was to develop an advanced GPS receiver chipset with high antijam capabilities. The program, initiated in 1985, has provided the technology for miniature receiver products for both unmanned and manned vehicle applications. A two-channel version of the receiver is in full-scale development for tactical missile applications. A five-channel version is being tested and evaluated as a drop-in replacement for RCVR-3A, the US Department of Defense standard high dynamic receiver. The NGR design started with the digital signal processing architecture developed for the Defense Advanced Research Project Agency (DARPA) hand-held GPS receiver. Enhancements were made to improve the antijam and signal acquisition performance. Producible, qualifiable and cost-effective silicon monolithic microwave integrated circuits and semicustom digital technologies were used to develop the core GPS chipset. A system design approach was established to permit reuse of mature and validated GPS software     

STEREO Ground Segment, Science Operations, and Data Archive

Vitally important to the success of any mission is the ground support system used for commanding the spacecraft, receiving the telemetry, and processing the results. We describe the ground system used for the STEREO mission, consisting of the Mission Operations Center, the individual Payload Operations Centers for each instrument, and the STEREO Science Center, together with mission support from the Flight Dynamics Facility, Deep Space Mission System, and the Space Environment Center. The mission planning process is described, as is the data flow from spacecraft telemetry to processed science data to long-term archive. We describe the online resources that researchers will be able to use to access STEREO planning resources, science data, and analysis software. The STEREO Joint Observations Program system is described, with instructions on how observers can participate. Finally, we describe the near-real-time processing of the “space weather beacon” telemetry, which is a low telemetry rate quicklook product available close to 24 hours a day, with the intended use of space weather forecasting.     

Magnetic reconnection in solar coronal loops

Simulations of the evolution of kink modes in line-tied coronal loops are presented which demonstrate the occurrence of magnetic reconnection in the non-linear stage of the instability. In loops which do not carry a net axial current (and are confined by a potential purely axial field) the reconnection is limited to the initial current-carrying channel and no overall loss of confinement is observed. In loops which carry a net current on the other hand, reconnection progressively involves field lines at greater and greater distances from the axis and even regions where the field was initially potential, leading to a total disruption of the magnetic field topology.     

A Series of Proton Flares in July 1985 from Observations by the Prognoz-10 Satellite and Vega-1, 2 Spacecraft

The enhancements of solar protons with an energy of more than 30 MeV, originating from flares in one active region and observed simultaneously aboard three spacecraft Vega-1, 2 and Prognoz-10 in July 1985, are analyzed and approximated in this work by using the reflection model [2]. The numerical values of several physical parameters (the parameters of distribution of solar cosmic ray (SCR) particles inside heliosphere traps, the coefficients of trap transparency) that are not observed by direct measurements are estimated.     

Effects of air current speed on gas exchange in plant leaves and plant canopies.

To obtain basic data on adequate air circulation to enhance plant growth in a closed plant culture system in a controlled ecological life support system (CELSS), an investigation was made of the effects of the air current speed ranging from 0.01 to 1.0 m s-1 on photosynthesis and transpiration in sweetpotato leaves and photosynthesis in tomato seedlings canopies. The gas exchange rates in leaves and canopies were determined by using a chamber method with an infrared gas analyzer. The net photosynthetic rate and the transpiration rate increased significantly as the air current speeds increased from 0.01 to 0.2 m s-1. The transpiration rate increased gradually at air current speeds ranging from 0.2 to 1.0 m s-1 while the net photosynthetic rate was almost constant at air current speeds ranging from 0.5 to 1.0 m s-1. The increase in the net photosynthetic and transpiration rates were strongly dependent on decreased boundary-layer resistances against gas diffusion. The net photosynthetic rate of the plant canopy was doubled by an increased air current speed from 0.1 to 1.0 m s-1 above the plant canopy. The results demonstrate the importance of air movement around plants for enhancing the gas exchange in the leaf, especially in plant canopies in the CELSS.