River restoration is something that is often used to help restore watercourses that were historically used for timber floating. In these restorations, instream wood (IW) plays a big role in increasing biodiversity and habitat heterogeneity in watercourses. Uncrewed Aerial Vehicles (UAVs) have proven to be useful when monitoring changes following river restoration but there is a need for less time-consuming methods to detect IW. This study’s objective was to investigate IW following a river restoration in an alluvial reach in Vargån, Northern Sweden and how well UAVs can be used to do this. Manual digitizing of IW was done in GIS from orthomosaics of three different flight occasions: pre-restoration, directly after and one year after restoration. An object- and color-based automated image thresholding was done to investigate if it could be used to automatically detect IW. The results showed that there were differences in number of IW, volume, width, and length between the different flight occasions. There was also indication that there had been movement of IW as well as changes in cluster composition, with more clusters with a higher number of wood pieces in the latest flight occasion. The automated image thresholding was able to accurately detect IW with an accuracy of 47,4 %, but it had limitations due to natural conditions. However, it showed the possibility of using automated methods to detect IW and with improvements it could become a faster and more accessible way of detecting IW in river monitoring.

In wireless communications, employing pilot symbols enables to estimate the state of the wireless channel at the expense of decreasing the number of symbols available for transmitting data. Addressing this trade-off is particularly challenging when the channel changes rapidly over time, since channel estimates become obsolete over short transmission periods. This master thesis proposes an analytical model to characterize this trade-off and develops an algorithm to find the near-optimal pilot spacing in terms of the achieved over spectral efficiency. This algorithm is simulated in a cellular system that serves uncrewed aerial vehicles. Numerical results indicate that the altitude of the uncrewed aerial vehicle, the Rician factor, the Doppler frequency, and the number of receive antennas influence the overall spectral efficiency and consequently, pilot spacing should take into account these system parameters. / I trådlös kommunikation möjliggör användning av pilotsymboler att uppskatta tillståndet för den trådlösa kanalen på bekostnad av att minska antalet tillgängliga symboler för att överföra data. Att ta itu med denna avvägning är särskilt utmanande när kanalen ändras snabbt över tiden, eftersom kanaluppskattningar blir föråldrade under korta överföringsperioder. Denna masteruppsats föreslår en analytisk modell för att karakterisera denna avvägning och utvecklar en algoritm för att hitta det närmast optimala pilotavståndet i termer av uppnådd över spektral effektivitet. Denna algoritm simuleras i ett cellulärt system som betjänar obemannade flygfarkoster. Numeriska resultat indikerar att höjden för det obemannade luftfartyget, Rician-faktorn, Dopplerfrekvensen, antalet mottagarantenner påverkar den totala spektrala effektiviteten och följaktligen bör pilotavståndet ta hänsyn till dessa systemparametrar.