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Ranging in an underwater medium with multiple isogradient sound speed profile layers.

Ramezani H, Leus G - Sensors (Basel) (2012)

Bottom Line: In this paper, we analyze the problem of acoustic ranging between sensor nodes in an underwater environment.The underwater medium is assumed to be composed of multiple isogradient sound speed profile (SSP) layers where in each layer the sound speed is linearly related to the depth.Furthermore, each sensor node is able to measure its depth and can exchange this information with other nodes.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, The Netherlands. h.mashhadiramezani@tudelft.nl

ABSTRACT
In this paper, we analyze the problem of acoustic ranging between sensor nodes in an underwater environment. The underwater medium is assumed to be composed of multiple isogradient sound speed profile (SSP) layers where in each layer the sound speed is linearly related to the depth. Furthermore, each sensor node is able to measure its depth and can exchange this information with other nodes. Under these assumptions, we first show how the problem of underwater localization can be converted to the traditional range-based terrestrial localization problem when the depth information of the nodes is known a priori. Second, we relate the pair-wise time of flight (ToF) measurements between the nodes to their positions. Next, based on this relation, we propose a novel ranging algorithm for an underwater medium. The proposed ranging algorithm considers reflections from the seabed and sea surface. We will show that even without any reflections, the transmitted signal may travel through more than one path between two given nodes. The proposed algorithm analyzes them and selects the fastest one (first arrival path) based on the measured ToF and the nodes' depth measurements. Finally, in order to evaluate the performance of the proposed algorithm we run several simulations and compare the results with other existing algorithms.

No MeSH data available.


Related in: MedlinePlus

(a) Number of paths versus the location of the two nodes. (b) Range error due to the linear approximation of the ToF.
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f5-sensors-12-02996: (a) Number of paths versus the location of the two nodes. (b) Range error due to the linear approximation of the ToF.

Mentions: In Figure 5(a), we show how many rays can travel between two points located in an unbounded two-layer underwater medium. Here, we imagine that the two layers have the same steepness but with different signs, e.g., a1 = −a2 = 0.1, and consequently the SSP has a minimum value at the boundary of the two layers. The sound speed at the boundary (z = 0) is assumed to be 1,480 m/s. To compute the number of possible rays between two points, we fix the position of xS, and change the position of xE to cover a 100 m by 3.5 km area in the vertical plane as depicted in the figure. According to the discussed lemmas, the possible patterns that can propagate between these two points are 1.2, 1.2.1.2, 1.2.(1.2)…, or 1.1, 1.2.1, 1.(2.1)…, depending on where the two points are located. It is shown that as the pair-wise distance between the two nodes which are located close to the boundary of the two layers increases, the number of paths between them increases too. Around the region where SSP has a minimum value, a pattern with lower number of digits has a lower ToF, but a greater overshoot. Therefore, to compute the fastest ray in this region we can start searching with a simple pattern, and check Lemma 3. If Lemma 3 holds, then we can stop, otherwise we should continue with a more complicated pattern.


Ranging in an underwater medium with multiple isogradient sound speed profile layers.

Ramezani H, Leus G - Sensors (Basel) (2012)

(a) Number of paths versus the location of the two nodes. (b) Range error due to the linear approximation of the ToF.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376626&req=5

f5-sensors-12-02996: (a) Number of paths versus the location of the two nodes. (b) Range error due to the linear approximation of the ToF.
Mentions: In Figure 5(a), we show how many rays can travel between two points located in an unbounded two-layer underwater medium. Here, we imagine that the two layers have the same steepness but with different signs, e.g., a1 = −a2 = 0.1, and consequently the SSP has a minimum value at the boundary of the two layers. The sound speed at the boundary (z = 0) is assumed to be 1,480 m/s. To compute the number of possible rays between two points, we fix the position of xS, and change the position of xE to cover a 100 m by 3.5 km area in the vertical plane as depicted in the figure. According to the discussed lemmas, the possible patterns that can propagate between these two points are 1.2, 1.2.1.2, 1.2.(1.2)…, or 1.1, 1.2.1, 1.(2.1)…, depending on where the two points are located. It is shown that as the pair-wise distance between the two nodes which are located close to the boundary of the two layers increases, the number of paths between them increases too. Around the region where SSP has a minimum value, a pattern with lower number of digits has a lower ToF, but a greater overshoot. Therefore, to compute the fastest ray in this region we can start searching with a simple pattern, and check Lemma 3. If Lemma 3 holds, then we can stop, otherwise we should continue with a more complicated pattern.

Bottom Line: In this paper, we analyze the problem of acoustic ranging between sensor nodes in an underwater environment.The underwater medium is assumed to be composed of multiple isogradient sound speed profile (SSP) layers where in each layer the sound speed is linearly related to the depth.Furthermore, each sensor node is able to measure its depth and can exchange this information with other nodes.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, The Netherlands. h.mashhadiramezani@tudelft.nl

ABSTRACT
In this paper, we analyze the problem of acoustic ranging between sensor nodes in an underwater environment. The underwater medium is assumed to be composed of multiple isogradient sound speed profile (SSP) layers where in each layer the sound speed is linearly related to the depth. Furthermore, each sensor node is able to measure its depth and can exchange this information with other nodes. Under these assumptions, we first show how the problem of underwater localization can be converted to the traditional range-based terrestrial localization problem when the depth information of the nodes is known a priori. Second, we relate the pair-wise time of flight (ToF) measurements between the nodes to their positions. Next, based on this relation, we propose a novel ranging algorithm for an underwater medium. The proposed ranging algorithm considers reflections from the seabed and sea surface. We will show that even without any reflections, the transmitted signal may travel through more than one path between two given nodes. The proposed algorithm analyzes them and selects the fastest one (first arrival path) based on the measured ToF and the nodes' depth measurements. Finally, in order to evaluate the performance of the proposed algorithm we run several simulations and compare the results with other existing algorithms.

No MeSH data available.


Related in: MedlinePlus