A temporal waterline approach to mapping intertidal areas using X-band marine radar

Paul S Bell,Cai O Bird,Andrew J Plater

doi:10.1016/j.coastaleng.2015.09.009

Paul S Bell, Cai O Bird + Show 1 more

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https://doi.org/10.1016/j.coastaleng.2015.09.009

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Abstract

Mapping the morphology of intertidal areas is a logistically challenging, time consuming and expensive task due to their large expanse and difficulties associated with access. A technique is presented here that uses standard marine navigational radar operating at X-band frequency. The method uses a series of time-exposure radar images over the course of a two-week tidal cycle to identify the elevation of the wetting and drying transitions at each pixel in the radar images, thereby building up a morphological map of the target intertidal area. This “Temporal Waterline” method is applied to a dataset acquired from Hilbre Island at the mouth of the Dee Estuary, UK, spanning March 2006 to January 2007. The radar gathered data with a radial range of 4km and the resulting elevation maps describe the intertidal regions of that area. The results are compared with airborne LiDAR data surveyed over the same area and within the radar survey time period. The residual differences show good agreement across large areas of beach and sandbanks, with concentrations of poor estimations around points that are shadowed from the radar or likely to suffer from pooling water. This paper presents the theoretical framework of the method and demonstrates its stability and accuracy. The Temporal Waterline radar method is aimed at providing a useful tool for the monitoring and operational management of coastlines.

Highlights

IntroductionShallow water environments are important to commercial activities as they are often the site of ports, harbours and recreational areas which represent high value assets in the provision of various ecosystem services and are the foundation of many local and national economies
This paper describes and presents a novel technique for mapping the changes in intertidal coastal morphology across varying timescales using standard marine radar operating at X-band, providing much needed situational awareness in intertidal areas and utilising existing port infrastructure, whilst keeping operational costs to a minimum
The accuracy relative to a LiDAR survey varies from an over-estimate of 0.12 m within the first 0.75 km from the radar, to an approximately 0.5 m over-estimate further from the radar, these comparisons are complicated by the complex nature of the macrotidal estuary used as the test case

Summary

Introduction

Shallow water environments are important to commercial activities as they are often the site of ports, harbours and recreational areas which represent high value assets in the provision of various ecosystem services and are the foundation of many local and national economies. These shallow water systems are incredibly dynamic and their morphology is known to change significantly during high energy storm events, and more gradually during average conditions. Sand bank migration rates of up to 250 m/year have been observed here (Fernandes et al, 2007), causing significant disruption to the operation of the ports

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