Ice–ocean interactions at Greenland Ice Sheet outlet glaciers exert critical control on ice-sheet mass loss and, consequently, global sea-level rise. The GEOEO North of Greenland 2024 icebreaker expedition acquired a breadth of data in the unsurveyed Victoria Fjord, north-western Greenland, to assess the causes of the rapid break-up of the C.H. Ostenfeld ice tongue in 2002, and the environmental changes since. The observations reveal inflows of warm (>0 °C) Atlantic water reaching the grounded ice margin. We propose that Atlantic warm water pulses entering the Arctic Ocean reach north-western Greenland, where they interact with glacier fronts, enhance ice discharge, and amplify the climate-driven retreat of marine-terminating glaciers. The collapse of C.H. Ostenfeld’s ice tongue, unlike the slower retreats of the ice tongues of neighbouring Petermann and Ryder glaciers, reflects unimpeded Atlantic water inflow due to the absence of a shielding bathymetric sill, a function of the region’s bedrock geology.

Underwater communication and networking are key enabling technologies for many current and future marine applications. Generally, the envisioned applications include environmental monitoring, aquaculture, and surveillance. On a practical level, these applications may incorporate static sensor platforms, unmanned underwater vehicles, manned and unmanned surface vehicles, and remotely controlled underwater vehicles. Long-range communication between sensors and vehicles underwater involves mapping digital information into acoustic signals that are transmitted using Piezo-electric transducers. Transmitting information acoustically is very energydemanding and is a limiting factor in several applications that comprise batterypowered systems. Further, the usable bandwidth is very narrow, typically providing data rates on the order of 0.1–1.0 kilobits/second. These are two out of several challenges to consider in network protocol design. This thesis’s main focus has been enhancing the applicability of flooding-based routing protocols by dynamically controlling the modems’ transmission powers and adaptively selecting the fastest possible communication method. Simulations and field experiments have shown that a distributed k-Nearest Neighbor Power Controller can achieve significant energy savings. Further experiments of a distributed link adaptation method with minimal overhead have achieved improved channel utilization and throughput in a time-varying environment. Lastly, as heterogeneous systems of vehicles and sensor platforms generally incorporate diverse communication hardware with different capabilities, they must negotiate what method and parameters to use before any actual data can be transferred. Herein, a promising method that could be used for this negotiation process in a ”first-contact” protocol was also evaluated through field experiments.

To make full use of the underwater acoustic channel, a high degree of adaptivity is typically required. A novel framework for efficient evaluation of link adaptation employing channel replay simulation with Watermark and a lookup table is proposed. The approach is used to compare link adaptation based on SNR and CRC feedback using measured sea data. The best performance is obtained with a CRC criterion since it detects if a communication link has poor behaviour. The method is further improved by introducing a memory mechanism that disables a link with repeated low reliability.

Systems of heterogeneous underwater vehicles and sensor platforms are being used in various applications. Although these systems are still deployed at a relatively small scale, rapid technological development is in progress, and a significant impact of these systems is approaching. To a large degree, this is driven by a desire to utilize the oceans for sustainable food, energy, and environmental monitoring. Vehicles and platforms in these systems communicate wirelessly using acoustic signals due to the limited range of radio signals. To form underwater networks, the systems must communicate at the same frequency range and use common network protocols. Flooding-type network protocols are easy to implement, robust, and can serve as a baseline for heterogeneous networks. Here, a transmission power controller used in conjunction with a flooding protocol is examined. Results show a great reduction in transmission power and potential for significant energy savings.

In this study, we present the first iteration of DPower, an energy conserving method for use in underwater acoustic networks. The method encompasses a straightforward transmission power calibration procedure and adaptive power level selection. The method was evaluated in combination with DFlood, a known and validated constrained flooding protocol developed for underwater applications. Simulations of a network with given prerequisites have shown that, with an acceptable increase in packet loss, the presented method can dramatically reduce the energy consumption and thus improve the life-time of networks. 

In this article, the problem of collaborative tracking of an underwater target using autonomous surface vehicles (ASVs) is studied. Distance-based formation control with a collision-avoidance potential function is employed as a solution. A formation control protocol is devised and applied to the formation tracking problem. With the protocol, the vehicles form a desired formation around a moving target in order to continuously estimate its position, while the centroid of the formation tracks the target. Almost global stability is proved for the case with three tracking agents. A fully operational platform with four ASVs was built to implement the derived algorithms. One of the vehicles was used to simulate a target and the rest to form a triangular formation around it. Power usage of a naval vessel is highly affected by water resistance forces which increases significantly with the velocity. This was accounted for by adding an additional term to the formation tracking protocol, thereby increasing the overall system endurance. Experimental results are presented.

In Arctic alpine regions, glacio-lacustrine environments respond sensitively to variations in climate conditions, impacting, for example,glacier extent and rendering former ice-contact lakes into ice distal lakes and vice versa. Lakefloors may hold morphological records of past glacier extent, but remoteness and long periods of ice cover on such lakes make acquisition of high-resolution bathymetric datasets challenging. Lake Tarfala and Kebnepakte Glacier, located in the Kebnekaise mountains, northern Sweden, comprise a small, dynamic glacio-lacustrine system holding a climate archive that is not well studied. Using an autonomous surface vessel, a high-resolution bathymetric dataset for Lake Tarfala was acquired in 2016, from which previously undiscovered end moraines and a potential grounding line feature were identified. For Kebnepakte Glacier, structure-from-motion photogrammetry was used to reconstruct its shape from photographs taken in 1910 and 1945. Combining these methods connects the glacial landform record identified at the lakefloor with the centennial-scale dynamic behaviour of Kebnepakte Glacier. During its maximum 20(th) century extent, attained c. 1910, Kebnepakte Glacier reached far into Lake Tarfala, but had retreated onto land by 1945, at an average of 7.9 m year(-1).

With regards to energy constrained Autonomous Underwater Vehicles (AUVs), and difficulties inherent to the acoustic underwater communication channel, a non-coherent method is investigated in order to improve energy consumption and reliability over traditional Frequency Shift Keying (FSK), without increasing the bandwidth. A proposed method of adapting Trellis Coded Modulation (TCM) to constant amplitude Permutated Frequency Shift Keying (PFSK) symbol constellations is evaluated. A system implementation of two PFSK methods is simulated in an Additive White Gaussian Noise channel, and field tested in an underwater channel in the Stockholm archipelago, where a binary FSK reference method is used as a comparison. The main interest is comparing electrical bit energy and bit error rate (BER) for the methods. Time variability of frequency fading, related to wind speed, is also evaluated from the field tests. 

This paper addresses the source localization problem of an acoustic fish-tag using the Time-of-Arrival measurement of an acoustic signal, transmitted by the fish-tag. The Time-of-Arrival measurements denote the pseudo-range information between the acoustic receiver and the fish-tag, except that the Time-of-Transmission of the acoustic signal is unknown. Starting with the pseudo-range measurement equation, a globally valid quasi-linear time-varying measurement model is presented that is independent of the Time-of-Transmission of the acoustic signal. Using this measurement model, an Uniformly Globally Asymptotically Stable (UGAS), three stage estimation strategy (eXogenous Kalman Filter) is designed to estimate the position of an acoustic fish-tag and evaluated against a benchmark Extended Kalman Filter based estimator. The efficacy of the developed estimation method is demonstrated experimentally, in presence of intermittent observations using an array of receivers mounted on three Unmanned Surface Vessels (USVs).

In this paper we present a proof-of-concept for an hydro acoustic fish-tag position estimation and tracking system. In our field-tested concept, a formation of Unmanned Surface Vehicles (USV) creates a mobile array of low-cost hydro acoustic fish-tag receivers. The array of receivers is able to estimate fish-tag locations and follow the fish on open waters, significantly increasing capabilities as compared to moored systems. The paper describes the system architecture and components in detail. It also evaluates the proof-of-concept characteristics based on the experience gathered during the field-test.