Advantages and limitations of using satellite images for flood mapping Domenico Grandoni e-geos Headquarter Contrada Terlecchie 75100 Matera - Italy Commercial Office Via Cannizzaro 71 00156 Roma - Italy Workshop on the Use of the Copernicus Emergency Service for Floods Brussels, October 21 th 2013 Material produced within GMES/Copernicus Emergency Management Service - Mapping in RUSH mode - funded by the EC budget (DG ENTR) Contract N. 257219
Satellite data for Earth Observation Optical satellites (e.g. Quickbird) Are affected by cloud coverage Acquire only during day time Because they have a passive sensor on board that needs light to record the image and that cannot see through clouds. MODIS, 16/10/2013 Page 2
Satellite data for Earth Observation Optical satellites (e.g. Quickbird) Can achieve a very high resolution (< 1m) But the higher the resolution, the smaller the coverage VHR1, < 1m resolution VHR2, 1 4 m resolution HR1, 4 10 m resolution Page 3
Satellite data for Earth Observation Optical satellites (e.g. Quickbird) Pass over any AOI once a day at 10:00 ca (local time) Because the second pass is at 22:00 ca (local time), but there is no light Page 4
Satellite data for Earth Observation Radar (SAR) satellites (e.g. COSMO-SkyMed) Are NOT affected by cloud coverage Acquire during day and night time MODIS, 16/10/2013 Because they have an active sensor on board that does not need light to record the image and that can see through clouds with almost any interaction. Radarsat-2, 16/10/2013 Page 5
Satellite data for Earth Observation Radar (SAR) satellites (e.g. COSMO-SkyMed) Can achieve a very high resolution (1m) But the higher the resolution, the smaller the coverage VHR2, 3m resolution HR2, 12m resolution Page 6
Satellite data for Earth Observation Radar (SAR) satellites (e.g. COSMO-SkyMed) Pass over any AOI twice a day at 07:00 ca (local time) Because they can exploit both day and night passes Page 7
Satellite data access - Time All Earth Observation satellite systems have time constraints for both: Acquiring images: OPTICAL Satellites: one pass/day at 10:00 ca local time SAR Satellites: two passes/day at 07:00 and 19:00 ca local time Uplink the acquisition plan to the satellite: OPTICAL Satellites: in general up to 6 hours* prior to pass (best case: 30 mins) SAR Satellites: in general up to 18 hours* prior to pass (best case: 6 hours) *Times expressed are indicative and depend on the satellite mission, the area to be acquired and the time of request submission In case of an activation over EU received at 12:00 on Day-0 : First available OPTICAL pass: 10:00 ca Day-1 First available SAR pass: 07:00 ca Day-1 (best case), 19:00 ca Day- 1 (normal case) Page 8
Access to Satellite data Actors GIO EMS RUSH Service Provider: Receives the SRF from DG ECHO/ERCC, refines AOIs together with AU and submit a generic Satellite data request (SPERF) to ESA (e.g. SAR VHR2 New Acquisition) ESA GEST: Receives the SPERF, contacts the relevant Satellite data commercial providers (GCMEs) and orders the most relevant satellite data within the requested category (e.g. Radarsat-2) Satellite Data Providers (e.g. MDA): Receive the tasking request from ESA and are responsible for the whole satellite data operations (planning, collection, production, delivery) Page 9
Access to Satellite data Workflow DAY 1 30th May 12:30 UTC SRF from AU 15:00 UTC GIO triggering (SRF) AOI negotiation 14:00 UTC SPERF to ESA 19:00 UTC SRT from ESA WV-2 images New 30/05/2013 AOI01 & AOI02 REJECTED by GSP Pleiades images New 31/05/2013 10:04 UTC AOI01 Delivered 18:00 UTC --> DELINEATION MAP AOI01 22:00 UTC Page 10
Access to Satellite data Main issues AOI Negotiation: ISSUE: If the received SRF is not well structured (1 OVR + 1 DTL min), Satellite data request to ESA cannot be transmitted and collection opportunies could be missed SOLUTION: SRF transmitted to GIO EMS RUSH service shall contain at least 1 OVR and 1 DTL AOIs at a consistent scale Cancellations from Satellite data providers: ISSUE: In case of techncial issues or conflict with other orders with higher priority, Sat. Providers can cancel tasking orders causing additional 24 hours delay SOLUTION: task multiple satellite missions as back up Delay in Satellite data delivery after collection: ISSUE: In some cases more than 10 hours after collection are wited before satellite image is delivered on FTP SOLUTION: - Slow data transfer rate: ISSUE: In some cases the data download speed is very low, introducing delays of hours before image can be analyzed SOLUTION: Control the download speed capabilities at the two ends Page 11
Satellite Flood Mapping - Principles Flood mapping from satellite imagery (Optical or SAR) is based on the following steps: 1. Extraction of the visible water extent from the post event image 2. Subtraction form the visible water extent of the extent of water bodies in normal conditions 1 2 Page 12
Flood mapping - Comparison Page 13
Flood Mapping Advantages/Limitations Satellite Flood mapping has the following advantages, compared to alternitives like in field or aerieal surveys: 1. Capability to acquire data everywhere in the world, covering a wide area in a very short time frame 2. Capability to acquire data under every weather condition and during night time (only SAR) 3. Capability to monitor the evolution of water retreat during the days/weeks following the event' with daily updates Satellite Flood mapping has the following limitations, compared to alternitives like in field or aerieal surveys: 1. Flood detection capability in urban and vegetated areas (SAR) 1. Due to resolution and active sensor limitations 2. Flood detection capability in forested areas (optical) 1. Due to passive sensor limitations 3. Flood detection capability in case of material presence (e.g. mudflows) Page 14
Limitations of SAR based flood mapping SAR based flood mapping is very effective when the standing water creates a flat surface In urban and forested areas the detection of standing water is disturbed by the presence of object that both prevent sensing (e.g. tree canopy) or alter the results (e.g. double bouncing effect, presence of material objects) Siem Reap, Cambodia Page 15
Thank you! www.e-geos.it Domenico Grandoni GIO EMS RUSH Service Provider Technical Manager +39 06 4079 3089 domenico.grandoni@e-geos.it Page 16