The pros and cons of topographic surveys using terrestrial or airborne platforms and their applicability in ICZM

• ¹ CIIMAR/Universidade do Porto, Portugal
• ² Faculdade de Ciências da Universidade do Porto, Departamento de Geociências, Ambiente e Ordenamento do Território, Portugal
• ³ Universidade de Trás-os-Montes e Alto Douro, Departamento de Matemática, Portugal
• ⁴ Faculdade de Ciências da Universidade do Porto, Observatório Astronómico, Portugal

Coastal zones are very dynamic land-ocean interfaces, shaped by natural and human factors. Coasts are often densely occupied and modified by man-made structures, changing their natural dynamics and their ability to adapt to changing environments. Over the last decades, coastal erosion has become a serious problem threatening not only local economies but also valuable habitats, such as dunes, lagoons and salt marshes. The assessment of coastal morphology and its dynamics is essential to quantify and understand changes, particularly those due to climate hazards and human intervention. We present several observation systems used to obtain digital elevation models: a video-based terrestrial mobile mapping system (MMS), a plane and two low-cost unmanned aerial vehicles (AUV) equipped with digital cameras. The systems are compared in terms of their features, the information they can provide and their applicability in ICZM. Methods differ in terms of: operating conditions, ease of deployment, costs (both in terms of time and money) and in the terrain and area they can cover. They also differ in precision (between less than 5 and 20 cm, depending on equipment and flight height), though all of the proposed systems are precise enough to assess changes in morphology that exceed short-term variations. Terrestrial mobile mapping systems are easy to deploy and suited to cover a few square kilometres, but they need adequate access. An airplane is much more efficient and less invasive. It covers any type of terrain but implies more costs, logistics and equipment. UAV, like delta wings and small helicopters are better suited for small areas. Delta wings are faster, but helicopters are more flexible in their movement. They are limited by battery life, and cannot be used with stronger winds (above ~20 km/h). The choice of an observation system will depend on the specific survey objectives and on the characteristics of the surveyed area. Type and accessibility of the area, its size, and the expected rates of change (fast changes require more frequent, i.e. easier to deploy, monitoring) have to be considered, next to the availability of equipment and expertise.