Satellite monitoring of urban growth at La Reunion: insights from Pleiades imagery

Transcription

1 Pleiades DAYS, April 1th-3rd 2014 Satellite monitoring of urban growth at La Reunion: insights from Pleiades imagery Thibault Catry 1 & Alain Besnard 2 1 SEAS-OI, UMR 228 Espace-Dev(UM2, UR, UAG, IRD), 40 Avenue de Soweto, CS70651, Saint-Pierre Cedex 2 DEAL Réunion, 2, rue Juliette Dodu Saint-Denis messagcedex 9 Toulouse, April 3rd 2014

2 Foreword: the SEAS-OI station SEAS-OI has been operating since July 2012 Antenna Operational center St-Pierre SEAS-OI SPOT 5 image of La Reunion SEAS-OI = Survey of the Environment Assisted by Satellite in the Indian Ocean

3 Foreword: SEAS-OI missions and research topics REGIONAL COOPERATION : scientific and operational projects in remote sensing DECISION SUPPORT : Indian Ocean spatial observatory Sustainable development SKILLS TRANSFER : training in remote sensing and GIS RESEARCH AND EDUCATION : environment Health climate risks Agroforestryand biodiversity Natural disasters Coastal environment and climate change Urbandynamicsand territorial vulnerability Healthand environment

4 Content Introduction Evolution of urbanareas from1997 to 2008: whatwelearn from aerial photographies and GIS approach Evolution of urban areas from 2008 to 2013: insights from Pleiades imagery and object-oriented approach Aerialphotographies vs. Pleiadesimages: advantagesand drawbacks for urban studies Conclusions Prospects

5 Introduction

6 Introduction 24 municipalities(main cities: St-Denis and St-Pierre) 2500 km 2 wideterritory

7 Introduction More than inhabitants, high density of population on the coasts of La Reunion

8 Introduction Being a threat to protected areas of La Reunion, urban growth has to bemonitored

9 Evolution of urban areas from 1997 to 2008: what we learn from aerial photographies and GIS approach (DEAL Reunion)

10 Evolution of urban areas between 1997 and 2008 Study carried out by the DEAL and AGORAH (Reunion) Source data: 1997, 2003 and 2008 IGN BD Ortho and BD Topo DEAL= Direction de l Aménagement, de l Equipement et du Logement AGORAH= Agence pour l'observation de la Réunion, de l'aménagement et de l'habitat DEAL AGORAH = GIS approach Ortho year Space resolution (m)

11 Evolution of urban areas between 1997 and 2008 Study carried out by the DEAL and AGORAH of La Reunion Source data: 1997, 2003 and 2008 IGN BD Ortho and BD Topo The example of Saint-Denis BD Ortho Space resolution = 1 m BD Ortho Space resolution = 0,5 m 5

12 Evolution of urban areas between 1997 and 2008 DEAL AGORAH = GIS approach Total surface of urbanareas in 2008 = ha + 27 % from1997 to % of urbanextension between1997 and 2008 occurredin the southof the island 55 % of urbanareas are low-densityperiurbanareas : no evolutionbetween1997 and 2008

13 Evolution of urban areas between 1997 and 2008 Densityof urban areas in 2008 DEAL AGORAH = GIS approach Between 1997 and 2008: 78 % growth of high-density urban areas 25 % growth of low-density urban areas Stability of peri-urban areas Geographical vatiability of these growth rates

14 Evolution of urban areas between 1997 and 2008 Densityof urban areas in 2008 The example of Saint-Denis

15 Evolution of urban areas between 1997 and 2008 DEAL, typicalurbanorganizationsfrom2008 aerialphotographies

16 Evolution of urban areas from 2008 to 2013: what we learn from Pleiades imagery and objectoriented approach (SEAS-OI)

17 Evolution of urban organization from 2008 to 2013 Last reports regardingurbanareas at La Reunionwerepublishedin 2010 and 2011 by the DEAL and AGORAH, on the basis of 2008 aerial photographies. Similarly, wecouldcompare 2008 and 2011 sets of aerialphotographies and BD Topo fromign, but

18 Evolution of urban organization from 2008 to 2013 Characterization of urban areas of Saint-Denis is made applying an object-oriented approachon a Pleiadesimage receivedin the frame of the CNES RTU 2013

19 Evolution of urban organization from 2008 to 2013

20 Evolution of urban organization from 2008 to 2013 Urbanarea # 1: high-density area Pléiades CNES(2013), DistributionAstriumServices /Spot Image S.A., France, tous droits réservés. Usage commercial interdit BD Ortho BD Topo IGN GIS approach Pleiades image Object-oriented approach urban area vegetation bare soil water Stabilityof surface and densityof type 1 urbanareas

21 Evolution of urban organization from 2008 to 2013 Urban area # 2: low-density area Pléiades CNES(2013), DistributionAstriumServices /Spot Image S.A., France, tous droits réservés. Usage commercial interdit BD Ortho BD Topo IGN GIS approach 2013 Pleiades image Object-oriented approach urban area vegetation bare soil Major changes in surface and densityof type 2 urbanareas : spaceisavailablefor urban development

22 Evolution of urban organization from 2008 to 2013 Urbanarea # 3: Peri-urban area Pléiades CNES(2013), DistributionAstriumServices /Spot Image S.A., France, tous droits réservés. Usage commercial interdit BD Ortho BD Topo IGN GIS approach Minorchanges in surface and densityof type 2 urbanareas : changes affect mainly nonpermanent buildings urban area vegetation bare soil 2013 Pleiades image Object-oriented approach 2013

23 Evolution of urban organization from 2008 to and BD Ortho BD Topo IGN GIS approach Ortho year Space resolution(m) Surface of urban areas = 5.8 km 2 Surface of urban areas = 5.8 km 2

24 Evolution of urban organization from 2008 to Pleiades image / Object-oriented approach Pléiades CNES(2013), Distribution Astrium Services /Spot Image S.A., France, tous droits réservés. Usage commercial interdit. Pleiades year Space resolution(m) Surface of urban areas = 6.9 m % between 2008 and 2013 urban area vegetation bare soil water Confusions: post-classification is required

25 Aerial photographies vs. Pleiades images: advantages and drawbacks for urban studies

26 Aerial photographies vs. Pleiades images Resolution in space 2008 orthophotographyand 2013 Pleiadesimage of Saint-Denis have the samespatial resolutionof 50 cm, whichisperfectyadaptedto the studyof urbanareas A 20 cm resolution such as the resolution of the 2011 orthophotography is not necessary Resolution in time IGN Orthophotographies, updated every 3 to 5 years, are poorly adapted to the precise study of urban dynamics at La Reunion, where changes occur rapidly. Pleiadesacquisition are more regularin time, makingpossible an annualupdate of urbanareas mapsof La Reunion, which is perfectly suitable in terms of urban dynamics and in accordance with the DEAL s wishes. Data treatment and processing Treatment of orthophotographies and GIS approach do not require either strong technical means or skills in image processing Treatmentof Pleiadesimages throughobject-orientedapproachrequirespowerfulcomputers and a good knowledge of remote sensing and image processing, a competency which does not exist among the institutional partners of SEAS-OI Objet-orientedapproachisfasterthanhandmadedigitilisation, but do to confusions post-classification process is required

27 Conclusions

28 Conclusions This studypresentedthe evolutionof urbanareas at La Reunion, fromthe exampleof its capital Saint Denis, where 3 types of urban organizations were identified. Similarevolutionfrom2003 to 2008 and from2008 to 2013: -strongstabilityof high-densityurbanareas whereconstructions are solidand permanent and no space is available for urban development -changes are concentratedon bothlow-densityareas and peri-urbanareas, where constructions can be more precarious and where space is available for urban development -competitionbetweenurbanareas and agricultural areas isa key to the future development of La Reunion Frequentupdates makepleiadesimages perfectlyadaptedto the studyof urbanareas and their rapid dynamics at La Reunion, but strong technical means and skills in remote-sensing and image processing are required The DEAL Reunion and AGORAH currently show strong interest in SPOT 5 and Pleiades images for land cover mapping at La Reunion, and are willing to integrate satellite approach in their future studies.

29 Prospects

30 Prospects Extendthe studyof urbanareas to all major citiesof La Reunion(Saint-Pierre, Saint-Paul, Saint-Benoît) using object-oriented methodologies applied to Pleiades images Theseimages werealreadyprovidedto SEAS-OI throughthe CNES RTU 2013 and thisworkisin progress The second stepto the studyof urbanareas isthe characterizationof urbantypologies within each of the 3 identified types of urban areas. Physical features of urban areas could be characterized combining Pleiades and SAR images. DEAL Reunionand itspartners, includingseas-oi, iscurrentlydeveloppinga tooland indicatorsfor the calculationof land use at La Reunion, basedon land covermapping. DEAL Reunion strongly relies on satellite imagery for this purpose and it is intended to realize land cover maps combining SPOT 5 and Pleiades images, with annual updates. This type of land covermapscouldberealizedon otherislandsof the southwesternindian Ocean basin, which is one important objective for SEAS-OI in the frame of regional cooperation.

31 Thank you for your attention