Author’s Accepted Manuscript Remote Sensing, Natural Hazards and the contribution of ESA Sentinels missions Dimitris Poursanidis, Nektarios Chrysoulakis
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To appear in: Remote Sensing Applications: Society and Environment Received date: 9 February 2016 Revised date: 18 September 2016 Accepted date: 21 February 2017 Cite this article as: Dimitris Poursanidis and Nektarios Chrysoulakis, Remote Sensing, Natural Hazards and the contribution of ESA Sentinels missions, Remote Sensing Applications: Society and Environment, http://dx.doi.org/10.1016/j.rsase.2017.02.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Remote Sensing, Natural Hazards and the contribution of ESA Sentinels missions Dimitris Poursanidis*, Nektarios Chrysoulakis Foundation for Research and Technology - Hellas (FORTH), Institute of Applied and Computational Mathematics, N. Plastira 100, Vassilika Vouton, 70013, Heraklion, Greece *
Corresponding author:
[email protected]
Abstract Natural hazards are phenomena with a large spatial dimension and impact. Their mapping and monitoring can be recorded only by using satellite remote image platforms. The range of the natural hazards and the way the latter affect the natural and manmade environments make the selection of the appropriate data types and analyses a challenging mission. Therefore, it is important that we understand the effects of each phenomenon as well as the potential relations between them, both in the temporal and spatial dimension. Furthermore, we take into account the availability and cost of the data in order to proceed to the selection of the appropriate data type and analysis as well as the potential of ESA’s Sentinel missions. All in all, this paper aims at examining the recent technological developments ever since the advent of Remote Sensing via a variety of platforms and the latter’s application for a better planning and confrontation of the natural hazards. Those which are of global interest and which occur more frequently during the last decades as a result of climate change are wild fires, flash floods in the urban and rural environments, landslides, tsunamis and soil erosion. Last but not least, the occurrence of volcanic activity, especially those in close proximity to urban areas, and heatwaves in the urban environment, are also mentioned.
Keywords: Natural hazards; Remote Sensing; Sentinels mission
1. Introduction Natural disasters and hazards whether triggered by natural or human factors, have become an issue of growing concern (Seneviratne et al., 2012, Prevention Web 2015). UNDRO in 1991 (UNDRO 1991) stated that population growth and land degradation are interrelated issues and as a consequence, more problems have arisen due to the uncontrollable expansion of housing in natural areas and high density unplanned urban sprawl. According to the recent annual review by the UNISDR (UNISDR 2015), 87% of the disasters are driven by the negative effects of climatic change in tandem with the degradation of natural resources. Both the frequency and magnitude of the disasters have posed a threat on the natural environment and its elements (biodiversity and its services) as well as the populations which live in diverse environments and especially those how are closer to urban and periurban – rural areas. Natural disasters like floods, drought and fire, landslides and desertification accompanied with soil erosion are highly related to human intervention. On the other hand, heatwaves, cyclones and tsunamis are phenomena driven by the climatic changes while volcanic explosions and earthquakes are purely natural phenomena. Deforestation for trade purposes or for unsustainable urban sprawl as well as other land cover alterations in the upstream parts of the catchments of the rivers change their hydrological regimes. Wildfires can, also, cause deforestation and may even result in massive destruction of properties and cultivations in rural areas. Deforested areas are susceptible to desertification due to bare land cover and intensive exploitation of the forthcoming new vegetation from pastoral activities if no management plans are applied in the areas. The above practices are responsible for landslides and flash floods downstream during the wet periods, with inconceivable ramifications to the urban environments. The most severe are socioeconomic impacts, including loss of human lives, health and quality of life degradation, loss of private and public property and a dramatic plunge in economic activities. The fact that the population density has increased is important. New settlements are gradually expanding in nearby problematic zones like areas along the river flood plains, marginal arid areas, and steep slopes susceptible to
landslides as well as to newly establish volcanic eruptions. Moreover, urban areas attract more people to live and work. The fast growing urban sprawl in tandem with a total lack in mitigation measures which will secure the quality of city life can become fatal when extreme temperatures occur for extended periods. This ultimately results in massive heatwaves which cause even deaths. The majority of the disasters are tackled as sudden emergency situations due to the total lack in emergency plans and risk maps in the areas, the underestimation of the hazard as well as the unusual and extreme conditions of the natural phenomena. The use of remote sensing when dealing with such natural disasters is a common practice nowadays (Li and Liu 2006, Voigt et al., 2007, Joyce et al., 2009, Joyce et al., 2014, Plank 2014). It is the only means that can provide large scale datasets for the support of the planning phase (Neuvel & den Brink 2009) and the risk assessment. Also, the datasets can be used for the evaluation of the post and after phase of a disaster, the spatial mapping in the aftermath of it as well as the support of the restoration and the evaluation of the economic impact. Remote sensing has increased its common use due to the growing interest in environmental issues as well as advances in geospatial technologies and the ability to provide the public with near real time imagery and information through different means, like the media and the web. At this point we shall discuss the approaches on the mapping and monitoring of a number of natural disasters like wildfires, floods, heatwaves and geological hazards (landslides, tsunamis and erosions) as well as the potential chain reaction between them. Optical Remote Sensing data from MODIS, Landsat, Aster, SPOT, IKONOS, WorldView and other satellite sensors producing imageries in a variety of spatial and temporal resolution have been extensively used for the identification of the hazards and the delineation of the boundaries of the affected areas as well as to support the restoration phase. When the weather conditions prevent the optical satellites from collecting data, the use of Synthetic Aperture Radar (SAR) satellites (Joyce 2014, Plank 2014) is the only option for the accurate and fast identification of the impacted areas. Radar satellites are operational over areas covered in clouds, in cases of floods, or smoke coverage due to wildfires as well as during the night as it uses microwave pulses in different wavebands for the collection of the information (Richards 2009). Both optical and
SAR data types can be collected by using airborne platforms (airplanes, UAVs) but the use of satellite collected data are much preferable due to the satellite’s extensive coverage and cost-affordability in collecting data as opposed to the airborne platforms. In the next sections we will provide information on the wildfires, floods and the so-called geological hazards, the heatwaves in the urban environment: the latter are for the first time mentioned in such a review was well as the contribution of the new Sentinel missions from the European Space Agency (ESA).
2. Wildfires
Even if a wildfire is a natural phenomenon which occurs in areas of combustible vegetation evident in forested-vegetated areas out in wilderness areas or in nearby cities and settlements, it is considered one of the most severe natural risks globally. South Europe, North America, Central Asia and Australia are the main areas on the planet that are annually affected with a number of variations during the fire seasons (IUCN 2000) This natural risk is a permanent threat for the natural resources with paramount ecological, economic and social ramifications, including the loss of lives and goods, damages to wildlife habitats, soil erosion and degradation of the watersheds. During the last decade the frequency, size and intensity of the fires in forests and forested areas has greatly increased (Jolly et al., 2015) as a result of global warming and degradation of natural resources because of man’s insatiable thirst for material possession. The quantification of the wildfire impact involves the delineation of the extend of the burnt area as well as the identification of the burn severity and the unburnt areas, the vegetated islets within the impacted area. The monitoring of the vegetation regeneration is crucial as is the cause of fire detection in the early stages, the forest fuel mapping prior to the fire in order to be used in fire modelling tools for early warning and planning as well as the monitoring of the vegetated habitats near the cityscapes.
Among the available satellite sources for wildfire scar mapping, optical data from MODIS (Kaufman et al., 1998, Justice et al., 2002, 2011, Giglio et al., 2003, Roy et al., 2008), Landsat missions (TM, ETM+, OLI) (Tucket et al., 2004, Potapov et al., 2015), Aster (Schroeder et al., 2008), SPOT (Silva et al., 2005, Gouveia et al., 2010) and IKONOS (Mitri & Gitas 2008) and WorldView II (Zhuoting et al., 2015) are among the most commonly used satellite images. In addition, SAR radar data from ALOS PALSAR, Radarsat-2, ERS-2, Envisat ASAR, COSMO-SkyMed and TerraSAR - X have been used for wildfire mapping (Bourgeau et al., Goodenough et al., 2011, Tanase et al., 2010, 2011, Mari et al., 2012, Millino et al., 2014, Avezzano et al., 2014). The synergy between optical satellite sensor data like the MODIS – Landsat synergy (Boscheti et al., 2015 and references cited in) is a novelty in order to increase the accuracy of the fire mapping or for the validation of the products of the lower resolution imageries with higher ones. This will become efficient after the availability of the Sentinel 2 constellation (2 satellites - 2A and 2B - on orbit) with a higher revisit time of 5 days during the phase of the constellation and with a spatial analysis of 10 meters in the visible spectrum. The Moderate Resolution Imaging Spectroradiometer (MODIS) is a multidisciplinary instrument, designed to measure physical and biological processes around the globe with a daily or every two days revision time. It acquires data in 36 bands from the visible to the thermal infrared spectrum with a spatial resolution from 250m to 1 km, and has been designed for a life span of 6 years. Two satellites from NASA, Terra and Aqua, carry MODIS instruments. Each one passes from the same location at different times during the day and, thus, it captures 2 images per day from the same location. It is used operationally by the Earth Observing System Data and Information System of NASA (NASA 2015a) as well as by the European Forest Fire Information System, EFFIS (Ayanz et al., 2012). EFFIS has been established by the Joint Research Centre (JRC) in order to support services in charge of the protection of forests against fires in the EU as well as to provide the EC services and the European Parliament with information on forest fires in Europe. EFFIS addresses forest fires in Europe in a comprehensive way, providing EU level assessments from pre-fire to post-
fire phases, thus supporting fire prevention, preparedness, firefighting and post-fire evaluations. For the fire detection, MODIS has a product, MOD 14 (Justice et al., 2011) through which thermal anomalies are detected. These are mainly due to Fires and Biomass burning and in this way the burnet areas can be mapped. MOD14 has a spatial resolution of 1km which is insufficient to detect and map small fire cases, for example, in cases of fires near or in rural areas. In addition it seems unable to identify unburnt islets within the delineated polygon of the fire (Sparks et al., 2015). However, a great advantage is its very high revisit time. The Aqua MODIS instrument acquires data two times per day, the same as Terra MODIS. Consequently, four daily MODIS fire observations are available for the accurate detection of a fire case as well as for the monitoring of the fire front in cases of large-scale fires. Landsat is the longest running program for the acquisition of satellite imagery on Earth. It was launched back in 1972 and now it is up with the Landsat OLI/TIRS or Landsat 8, named as the Landsat Continuity Mission (Roy et al., 2014) and the continuation of the Landsat mission has been secured after the planning for the Landsat 9 which will be in orbit in 2023 (NASA 2015b). Landsat data have a nominal resolution of 30 meters, 11 bands (depending of the mission) and a revisit time of 16 days. Over the course of wildfires, Landsat imagery is widely used for the assessment of the wildfire impact (Chuvieco & Congalton 1988, Haro et al., 2001, Veraverbeke et al., 2010, Bastarrika et al., 2011), the vegetation regeneration (Cohen et al., 2010, Veraverbeke et al., 2011) as well as for registering historical fires (Huang et al., 2010, Goodwin et al., 2014, Chen et al., 2014, Potapov et al., 2015) since the archive stores images back to the 1970s’. The high revisit time, high resolution and the above archive when compared to competitors like ASTER or previous Landsat sensors (Poursanidis et al, 2015), make the choice and use of the Landsat archive a unique means of wildfire mapping and the its impacts on a local scale as well as for the analysis of time series. The use of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite sensor data, even if it is equipped with better spatial resolution in the visible and NIR (15m) sensor, has limited uses (Petropoulos et al., 2010, Lasaponara et al., 2007b) due to its limited design to store
images inn a systematic manner as the user has to apply for any image acquisition on a specific day and time. In periodical times, ASTER imageries are archived and, under certain circumstances, suitable images for the needed periods can be found. MODIS, LANDSAT and ASTER satellite images are freely available for use from the scientific community as well as from the industry through their dedicated distribution portals. This makes them suitable for use in an operational way in order to monitor wildfires with the MODIS daily or every 16 days or whenever the atmospheric conditions are suitable for LANDSAT and ASTER uses. Yet, there is still a gap for additional data in these resolutions and at no cost. The SPOT (Satellite Probatoire d’Observation de la Terre) satellite program is a mission of Earth Observation satellites by the French Centre National d’ Etudes Spatiales (CNES). Seven SPOT satellites have been launched since 1986. SPOT 1-4 has a 10m spatial resolution in the panchromatic and 20m in the multispectral channels. SPOT 5 has 2.5m spatial resolution in the panchromatic and 10m in the multispectral channels while SPOT 6 & 7 have a 1.5m spatial resolution in both the panchromatic and multispectral channels. The existence of this constellation and the capability to capture images off-nadir, something that LANDSAT cannot, reduces significantly the revisit time of any geographic area. Thus, it is possible to have coverage of the same location on a daily basis. The use of SPOT satellite images is limited during wildfires due to the commercial operation of the satellites as well as to the small size of a standard scene (60 x 60 km) in comparison to the standard LANDSAT scene (170 x 185 km). Nevertheless, SPOT images have been used for the assessment of burn severity as well as the post-fire recovery of the vegetation in burnt areas (Fox et al., 2008, Sankey et al., 2008). The subsidization of the SPOT imageries is noted in the above-mentioned works since their cost in a multi-temporal or operational base is very high. The same is applied to Very High Resolution (VHR) satellite images like IKONOS, QUICKBIRD, WorldView (II, III) and others. They have a high spatial resolution (
