Advantages and limitations of using satellite images for flood mapping

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Advantages and limitations of using satellite images for flood mapping

Domenico Grandoni

Workshop on the Use of the Copernicus Emergency Service for Floods

Brussels, October 21th 2013

Material produced within GMES/Copernicus Emergency Management Service - Mapping in RUSH mode - funded by the EC budget (DG ENTR) – Contract N. 257219

Page 2e-GEOS Proprietary

Satellite data for Earth Observation

• Optical satellites (e.g. Quickbird)

Are affected by cloud coverage Because they have a passive sensor on board that needs light to record the image and that cannot “see” through clouds.Acquire only during day time

MODIS, 16/10/2013




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




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



• Radar (SAR) satellites (e.g. COSMO-SkyMed)

Are NOT affected by cloud coverage 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.

Acquire during day and night time

MODIS, 16/10/2013

Radarsat-2, 16/10/2013




Can achieve a very high resolution (1m) But the higher the resolution, the smaller the coverage

VHR2, 3m resolution HR2, 12m resolution




Pass over any AOI twice a day at 07:00 ca (local time)

Because they can exploit both day and night passes


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)

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)

*Times expressed are indicative and depend on the satellite mission, the area to be acquired and the time of request submission


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)


Access to Satellite data – Workflow

30th May

DAY 1

14:00 UTCSPERF to ESA

15:00 UTCGIO

triggering(SRF)

12:30 UTCSRF from AU

19:00 UTCSRT from ESA

WV-2 images New 30/05/2013 AOI01 & AOI02

Pleiades images New 31/05/2013 10:04 UTC AOI01

REJECTED by GSP

Delivered 18:00 UTC --> DELINEATION MAP AOI01 22:00 UTC

AOI negotiation


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


Satellite Flood Mapping - PrinciplesFlood 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


Flood mapping - Comparison


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 duringnight 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)


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


Thank you!www.e-geos.it

Domenico Grandoni

GIO EMS RUSH

Service Provider Technical Manager

+39 06 4079 3089

[email protected]

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Advantages and limitations of using satellite images for flood mapping