Advantages and limitations of using satellite images for

Advantages and limitations of using satellite
images for flood mapping
Domenico Grandoni
Workshop on the Use of the Copernicus Emergency
Service for Floods
e-GEOS
Brussels, October 21th 2013
Headquarter
Contrada Terlecchie
75100 Matera - Italy
Commercial Office
Via Cannizzaro 71
00156 Roma - Italy
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
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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
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Satellite data for Earth Observation
• Optical satellites (e.g. Quickbird)
Pass over any AOI once a day at 10:00 ca Because the second pass is at 22:00
ca (local time), but there is no light
(local time)
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Satellite data for Earth Observation
• Radar (SAR) satellites (e.g. COSMO-SkyMed)
Are NOT affected by cloud coverage
Acquire during day and night time
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.
MODIS, 16/10/2013
Radarsat-2, 16/10/2013
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Satellite data for Earth Observation
• Radar (SAR) satellites (e.g. COSMO-SkyMed)
Can achieve a very high resolution (1m)
VHR2, 3m resolution
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But the higher the resolution,
the smaller the coverage
HR2, 12m resolution
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Satellite data for Earth Observation
• Radar (SAR) satellites (e.g. COSMO-SkyMed)
Pass over any AOI twice a day at 07:00 ca Because they can exploit both day
(local time)
and night passes
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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 Day1 (normal case)
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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)
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Access to Satellite data – Workflow
DAY 1
30th May
15:00 UTC
GIO
triggering
(SRF)
12:30 UTC
SRF from AU
AOI
negotiation
14:00 UTC
SPERF to ESA
19:00 UTC
SRT from ESA
WV-2 images New 30/05/2013 AOI01 & AOI02
Pleiades images New 31/05/2013 10:04 UTC
AOI01
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REJECTED by GSP
Delivered 18:00 UTC --> DELINEATION MAP AOI01 22:00 UTC
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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
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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
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2
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Flood mapping - Comparison
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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)
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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
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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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