8 results on '"Mohammadloo, Tannaz H."'
Search Results
2. Geometrically constrained kinematic global navigation satellite systems positioning: Implementation and performance
- Author
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Asgari, Jamal, Mohammadloo, Tannaz H., and Amiri-Simkooei, Ali Reza
- Published
- 2015
- Full Text
- View/download PDF
3. Assessing the Performance of the Phase Difference Bathymetric Sonar Depth Uncertainty Prediction Model.
- Author
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Mohammadloo, Tannaz H., Geen, Matt, S. Sewada, Jitendra, Snellen, Mirjam, and G. Simons, Dick
- Subjects
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PREDICTION models , *SONAR - Abstract
Realistic predictions of the contribution of the uncertainty sources affecting the quality of the bathymetric measurements prior to a survey is of importance. To this end, models predicting these contributions have been developed. The objective of the present paper is to assess the performance of the bathymetric uncertainty prediction model for Phase Difference Bathymetric Sonars (PDBS) which is an interferometric sonar. Two data sets were acquired with the Bathyswath-2 system with a frequency of 234 k Hz at average water depths of around 26 m and 8 m with pulse lengths equal to 0.0555 m s and 0.1581 m s , respectively. The comparison between the bathymetric uncertainties derived from the measurements and those predicted using the current model indicates a relatively good agreement except for the across-track distances close to the nadir. The performance of the prediction model can be improved by modifying the term addressing the effect of footprint shift, i.e., spatial decorrelation, on the bottom due to fact that at a given time the footprints seen by different receiving arrays are slightly different. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
4. Inversion of sound speed profiles from MBES measurements using Differential Evolution.
- Author
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Keyzer, Lennart, Mohammadloo, Tannaz H., Snellen, Mirjam, Pietrzak, Julie, Katsman, Caroline, Afrasteh, Yosra, Guarneri, Henrique, Verlaan, Martin, Klees, Roland, and Slobbe, Cornelis
- Subjects
DIFFERENTIAL evolution ,SPEED of sound ,ORTHOGONAL functions ,MULTIBEAM mapping ,WATER depth ,OCEAN temperature - Abstract
The sound speed provides insight in ocean properties, as it depends on depth, temperature and salinity. Here, we propose a method to invert sound speed profiles (SSPs) from multibeam echosounder (MBES) measurements, providing a SSP for every ping. Using erroneous SSPs results in a mismatch in the estimated bathymetry between overlapping swaths. The SSP is estimated by minimizing this mismatch using Differential Evolution. In this work, SSPs are described using empirical orthogonal functions (EOFs), which are obtained from historical SSPs. As a proof-of-concept, we apply the inversion on a simulated MBES survey, where the synthetically generated SSPs are fully described by 3 EOFs. The inverted SSPs deviate 1 m/s from the correct profiles. In the case of actual SSPs, more EOFs are possibly required. The number of required EOFs to get an accurate estimate of the SSP is assessed by using SSPs acquired in the North Sea. Results show that including only 2 EOFs is sufficient to accurately estimate the SSP, although larger deviations up to 3 m/s were found. In this paper, we demonstrated the potential of the proposed method to invert SSPs from MBES measurements, which can provide information about the vertical structure of the water column. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
5. Assessment of reliability of multi-beam echo-sounder bathymetric uncertainty prediction models
- Author
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Mohammadloo, Tannaz H., Snellen, M., Amiri Simkooei, A., Simons, D.G., and Papadakis, John S.
- Subjects
Inherent MBES Uncertainty Sources ,Multibeam Echosounder Derived Depth ,Bathymetric Uncertainty Prediction - Abstract
Nowadays Multi-Beam Echo-Sounder (MBES) systems are used for obtaining information of the sea/river bed bathymetry and sediment composition. For the latter, use is usually made of the backscatter strength and depth derivatives, such as depth residuals. However, the depth derivatives are affected by the uncertainties inherent to the MBES varying with the sensors used, survey configuration and operational environment. Although models are available for the vertical uncertainty prediction, the question is how well these models can capture the estimated uncertainties of real observations. The present contribution addresses this issue by comparing the measured with modelled depth uncertainty accounting for the most recent insights of the error contributors. Data was acquired in water depths of around 2m, 10m and 30m with pulse lengths of 27 μs, 54 μs and 134 μs in the Oosterschelde estuary, the Netherlands, enabling the assessment of depth and pulse length dependence of the uncertainties. In general, the predicted and measured uncertainties are in the same order of magnitude. With increasing depth the discrepancy between the modelled and measured uncertainties increases. The effect of changing pulse length is found to be captured by the model, except for the angles close to nadir. The most dominant contributors to the vertical uncertainty are those induced by the angle of impact and range measurements. These contributors thus require further investigation to obtain a more realistic estimate of the vertical uncertainties.
- Published
- 2019
6. Automated Correction of Refraction Residuals
- Author
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Beaudoin, Jonathan, Renoud, Weston, Mohammadloo, Tannaz H., and Snellen, M.
- Abstract
In a world of high precision sensors, one of the few remaining challenges in multibeam echosounding is that of refraction-based uncertainty. A poor understanding of oceanographic variability or a poor choice of equipment can lead directly to poor quality bathymetric data. Post-processing software tools have existed for some time to allow data processors to correct for these artifacts. These tools typically involve the manual review of soundings and manual adjustment of a small set of parameters to achieve the desired correction. Though there are a number of commercial solutions currently available, they all have the same inherent weaknesses: (1) they are manual, thus time-consuming, (2) they are subjective, thus not repeatable, (3) they require expert training and thus are typically only usable by experienced personnel. QPS and the Technical University of Delft, The Netherlands (TU Delft) have worked together to implement an algorithm to address these issues in QPS’ post-processing software, Qimera. The algorithm, the TU Delft Sound Speed Inversion, works by taking advantage of the overlap between survey lines, harnessing the power of redundancy of the multiple observations. For a given set of pings, the algorithm simultaneously estimates sound speed corrections for the chosen pings and their neighbors by computing a best-fit solution that minimizes the mismatch in the areas of overlap between lines. This process is repeated across the entire spatial area, allowing for an adaptive solution that responds to changes in oceanographic conditions. This process is completely automated and requires no operator interaction or data review. The algorithm is also physics-based in that it honors the physics of acoustic ray bending. For accountability, the algorithm preserves the output of the inversion process for review, vetting, adjustment, and reporting. In this paper, we briefly explain how the algorithm works in simple terms. We also explore two data sets that cover differing oceanographic conditions, seabed morphologies, and survey line planning geometries in order to establish some early guiding principles on how far the algorithm can be pushed for performance.
- Published
- 2018
7. Assessing the repeatability of sediment classfication method and the limitations of using depth residuals
- Author
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Mohammadloo, Tannaz H., Tengku Ali, T.A., Snellen, M., Koop, L., Gaida, T.C., and Simons, D.G.
- Subjects
Acoustic seafloor classification (ASC) ,MBES inherent uncertainties, depth residuals ,Multibeam derived bathymetry - Abstract
Knowing the morphology and sediment composition of the seabed is of high importance for various applications. In this contribution, the repeatability of acoustic seafloor classification (ASC) results obtained from MBES backscatter value is investigated. The unsupervised classification algorithm based on Principal Component Analysis has been applied to the MBES backscatter acquired in the Cleaver Bank, Netherlands Continental Shelf, during five different surveys with two vessels. In general, there is good repeatability between surveys demonstrating the potential of using backscatter for marine environmental monitoring. To increase the discrimination performance the so-called depth residuals can be used. These are derived from the bathymetric measurements and considered to be representative for the sediment roughness. The challenge is that the small-scale depth variations are not solely dependent on the sediment roughness but also on the intrinsic uncertainties inherent to the MBES system. An A-Priori Multibeam Uncertainty Simulation Tool (AMUST) has been developed to predict the depth errors induced by various contributors. Correcting the measured depths for these uncertainties, as predicted by AMUST, theoretically provides information about the actual sediment roughness and this should improve the ASC algorithms. This was first tested on a MBES data set from Shallow Survey Conference Plymouth, 2015. It was shown that for the water depth of 20 m the standard deviation of the depth measurements was in agreement with AMUST predictions indicating a smooth seafloor, however, discrepancies between the predictions and real measurements occurred for the water depth of 8 m which is an indication of roughness or morphological features. This indicates the necessity of knowledge about the uncertainties when the objective is to derive the sediment roughness from MBES measurements.
- Published
- 2017
8. Mapping the Seabed and Shallow Subsurface with Multi-Frequency Multibeam Echosounders.
- Author
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Gaida, Timo C., Mohammadloo, Tannaz H., Snellen, Mirjam, and Simons, Dick G.
- Subjects
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OCEANOGRAPHIC maps , *MARINE sediments , *GEOLOGICAL modeling , *SPATIAL variation , *OCEAN bottom , *BATHYMETRY - Abstract
Multi-frequency multibeam backscatter (BS) has indicated, in particular for fine sediments, the potential for increasing the discrimination between different seabed environments. Fine sediments are expected to have a varying signal penetration within the frequency range of modern multibeam echosounders (MBESs). Therefore, it is unknown to what extent the multispectral MBES data represent the surface of the seabed or different parts of the subsurface. Here, the effect of signal penetration on the measured multi-frequency BS and bathymetry is investigated. To this end, two multi-frequency datasets (90 to 450 kHz) were acquired with an R2Sonic 2026 MBES, supported by ground-truthing, in the Vlietland Lake and Port of Rotterdam (The Netherlands). In addition, a model to simulate the MBES bathymetric measurements in a layered medium is developed. The measured bathymetry difference between the lowest (90 kHz) and highest frequency (450 kHz) in areas with muddy sediments reaches values up to 60 cm dependent on the location and incident angle. In spatial correspondence with the variation in the depth difference, the BS level at the lowest frequency varies by up to 15 dB for the muddy sediments while the BS at the highest frequency shows only small variations. A comparison of the acoustic results with the ground-truthing, geological setting and model indicates that the measured bathymetry and BS at the different frequencies correspond to different parts of the seabed. However, the low-frequency BS cannot be directly related to a subsurface layer because of a significant sound attenuation in the upper layer. The simulation of the MBES bottom detection indicates that the bathymetry measured at the highest and lowest frequency can be used to determine the thickness of thin layers (∼20 cm). However, with an increasing layer thickness, the bottom detection becomes more sensitive to the incident angle and small variations in the sediment properties. Consequently, an accurate determination of the layer thickness is hampered. Based on this study, it is highly recommended to analyze multi-frequency BS in combination with the inter-frequency bathymetry difference to ensure a correct interpretation and classification of multi-frequency BS data. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
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