Abstract-Automatic detection of human motion is important for security and surveillance applications. Compared to other sensors, radar sensors present advantages for human motion detection and identification because of their all-weather and day-and-night capabilities, as well as the fact that they detect targets at a long range. This is particularly advantageous in the case of remote and highly cluttered radar scenes. The objective of this paper is to investigate human motion in highly cluttered forest medium to observe the characteristics of the received Doppler signature from the scene. For this purpose we attempt to develop an accurate model accounting for the key contributions to the Doppler signature for the human motion in a forest environment. Analytical techniques are combined with full wave numerical methods such as Method of Moments (MoM) enhanced with Fast Multipole Method (FMM) to achieve a realistic representation of the signature from the scene. Mutual interactions between the forest and the human as well as the attenuation due to the vegetation are accounted for. Due to the large problem size, parallel programming techniques that utilize a Graphics Processing Unit (GPU) based cluster are used.

Detailed measurements of the rain phenomena can be obtained from modern equipment that provides experimental drop size distributions (DSDs), which can be used to analyze the effects of past rain events or to predict their influence on colocated radio links. In this letter, the use of experimental DSDs to predict rain effects on millimeter-wave propagation is discussed from a practical point of view, taking advantage of the availability of measurements from various instruments. The derived results show that predictions can be calculated with reasonable accuracy, provided that some practical considerations are taken into account.

This study is based on the results of a slant-path Ka-band propagation experiment carried out in Madrid, Spain, regarding rain attenuation, which is the main propagation impairment in this frequency band. The experimental and statistical results correspond to seven complete years of measurements, a period large enough to accomplish a comprehensive analysis in order to characterize the variability of rain rate and attenuation. It is shown that year-to-year variability is significant in temperate climates as Madrid's. The aforementioned significance is also apparent with regards to seasonal, monthly, worst-month and hourly variability concerning rain attenuation, which are also discussed and related when possible to the variability of the rain phenomena, either represented by the total amounts of rainfall in the different periods or by rain rate statistics.Report of COST Action 255 [4], or the more recent National Technical University of Athens model [5], or the Synthetic Storm Technique (SST) [6], in addition to the global models for rain rate included in ITU-R Rec. P. 837-6 [7]. Procedures to predict worst-month statistics from average-year predictions or measurements are described in ITU-R Rec. P. 841-4 [8].Thus, the variability of propagation phenomena is not well-addressed in propagation models. Regulatory documents, such as [9,10], partially deal with this subject, which is of growing interest, as shown for example in [11]. Studies on the variability of the propagation measurements from experimental results are very scarce, being [12][13][14] some of the few examples that can be found in the literature. Another approach is the simulation of propagation results starting from long-term rain rate data that are converted into attenuation data using the SST. The variability of the resulting propagation results can be analyzed as was performed, for example, in [15,16]. The variability of rain rate statistics has also been addressed in a few papers [17][18][19][20][21].In this paper, the variability of rain rate and rain attenuation is assessed, making use of the results of a long-term propagation experiment carried out in Madrid, Spain. The Ka-band beacon of the Eutelsat Hot Bird 13A satellite (previously known as Hot Bird 6) has been continuously measured since June 2006 to the first days of July 2013, when the beacon was switched off as part of the process of reconfiguring the satellite to a different orbital position. The period of measurements includes seven complete years, which allows a comprehensive characterization of the propagation channel. The minimum number of years of measurements needed to take into account the natural variability of the rain phenomena and their effects on propagation has been discussed for a long time. A study of long-term rain rate data [17] concludes that seven is the minimum number of years for which most of the averages (of individual distributions) fall within the 5-95% confidence limits of the long-term (49 years) distribution. According to this study, longer periods, such as 1...

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