Total ionizing dose and single event upset testing of flash based field programmable gate arrays

The effectiveness of implementing field programmable gate arrays (FPGAs) in communication, military, space and high radiation environment applications, coupled with the increased accessibility of private individuals and researchers to launch satellites, has led to an increased interest in commercial off the shelf components. The metal oxide semiconductor (MOS) structures of FPGAs however, are sensitive to radiation effects which can lead to decreased reliability of the device. In order to successfully implement a FPGA based system in a radiation environment, such as on-board a satellite, the single event upset (SEU) and total ionizing dose (TID) characteristics of the device must first be established. This research experimentally determines a research procedure which could accurately determine the SEU cross sections and TID characteristics of various mitigation techniques as well as control circuits implemented in a ProASIC3 A3P1000 FPGA. To gain an understanding of the SEU effects of the implemented circuits, the test FPGA was irradiated by a 66MeV proton beam at the iTemba LABS facility. Through means of irradiation, the SEU cross section of various communication, motor control and mitigation schemes circuits, induced by high energy proton strikes was investigated. The implementation of a full global triple modular redundancy (TMR) and a combination of TMR and a AND-OR multiplexer filter was found to most effectively mitigate SEUs in comparison to the other techniques. When comparing the communication and motor control circuits, the high frequency I2C and SPI circuits experienced a higher number of upsets when compared to a low frequency servo motor control circuit. To gain a better understanding of the absorbed dose effects, experimental TID testing was conducted by irradiating the test FPGA with a cobalt-60 (Co-60) source. An accumulated absorbed dose resulted in the fluctuation of the device supply current and operating voltages as well as resulted in output errors. The TMR and TMR filtering combination mitigation techniques again were found to be the most effective methods of mitigation

Influence of Drone Altitude, Image Overlap, and Optical Sensor Resolution on Multi-View Reconstruction of Forest Images

CITATION: Seifert, E., et al. 2019. Influence of drone altitude, image overlap, and optical sensor resolution on multi-view reconstruction of forest images. Remote Sensing, 11(10):1252, doi:10.3390/rs11101252.The original publication is available at http://www.mdpi.comPublication of this article was funded by the Stellenbosch University Open Access FundRecent technical advances in drones make them increasingly relevant and important toolsfor forest measurements. However, information on how to optimally set flight parameters and choosesensor resolution is lagging behind the technical developments. Our study aims to address this gap,exploring the effects of drone flight parameters (altitude, image overlap, and sensor resolution) onimage reconstruction and successful 3D point extraction. This study was conducted using video footageobtained from flights at several altitudes, sampled for images at varying frequencies to obtain forwardoverlap ratios ranging between 91 and 99%. Artificial reduction of image resolution was used to simulatesensor resolutions between 0.3 and 8.3 Megapixels (Mpx). The resulting data matrix was analysed usingcommercial multi-view reconstruction (MVG) software to understand the effects of drone variables on(1) reconstruction detail and precision, (2) flight times of the drone, and (3) reconstruction times duringdata processing. The correlations between variables were statistically analysed with a multivariategeneralised additive model (GAM), based on a tensor spline smoother to construct response surfaces.Flight time was linearly related to altitude, while processing time was mainly influenced by altitudeand forward overlap, which in turn changed the number of images processed. Low flight altitudesyielded the highest reconstruction details and best precision, particularly in combination with high imageoverlaps. Interestingly, this effect was nonlinear and not directly related to increased sensor resolution athigher altitudes. We suggest that image geometry and high image frequency enable the MVG algorithmto identify more points on the silhouettes of tree crowns. Our results are some of the first estimates ofreasonable value ranges for flight parameter selection for forestry applications.https://www.mdpi.com/2072-4292/11/10/1252Publisher's versio