gmes space component sentinel-1, -2 and...

GMES SPACE COMPONENT

SENTINEL-1, -2 AND -3

Peter G. Edwards, Guido Levrini, François Spoto, Bruno Berruti, Kurt Büchler

European Space Research and Technology Centre (ESTEC), Keplerlaan 1, Postbus 299,

2200 AG Noordwijk (The Netherlands)

Emails: [email protected], [email protected], [email protected],

[email protected], [email protected]

ABSTRACT

In the frame of the Global Monitoring for Environment

and Security (GMES) programme jointly implemented

by ESA and EC, ESA is developing the Sentinel-1, -2

and -3 satellites as part of the GMES Space Component

(GSC) system. The Sentinel satellites will provide

dedicated services alongside national and other missions

which contribute to GMES with the following

instruments and technologies:

• Sentinel-1: C-band interferometric radar

• Sentinel-2: Multispectral optical imaging

• Sentinel-3: Wide-swath, low-medium resolution

optical and infrared radiometers and a radar

altimeter package

Each Sentinel mission is based on a constellation of 2

satellites in the same orbital plane. The lifetime of the

individual satellite is specified as 7 years (with

consumables for 12). The life cycle of the space

segment is planned to be in the order of 15-20 years. A

description of the satellites and their payload

complement with the planned performance data is

given.

1. THE SENTINEL SATELLITES AND GMES

The objective of the Global Monitoring for

Environment and Security Space Component

programme is to fulfil the space-based observation

requirements in response to European policy priorities

with a particular emphasis on the “fast-track” services

identified by the EC for early implementation. It aims at

the provision of satellite data for these fast-track

services from 2008 onwards and the development,

launch and operations of dedicated infrastructure

(Sentinel satellites) with the corresponding ground

segment developments. The first Sentinel launch is

planned for 2011.

Currently three fast-track services - on land monitoring,

marine services and emergency response - are defined

by the EC’s Fast-Track Implementation Groups. The

Sentinel satellites are tailored for these services. To

fulfill revisit and coverage requirements, to provide a

robust operational service and to be affordable, each

Sentinel mission is based on a constellation of 2

satellites in the same orbital plane. The lifetime of the

individual satellite is specified as 7 years (with

consumables for 12). The life cycle of the space

segment is planned to be in the order of 15-20 years.

The strategy for Sentinel procurement and replacement

over this period is being elaborated, but will likely result

in a need for 4 or 5 satellites of each type if the desired

robustness for the service that GMES will provide is to

be achieved.

2. TECHNICAL KEY ELEMENTS OF THE

SENTINELS

Technical key success criteria for GSC include, aside

from the obvious need to complete the individual

missions to specification, in schedule and within cost,

the following specific issues related to the purpose of

the programme:

• Use of robust, state-of-the-art, technologies which

will minimise development risk and maximise

production schedule reliability, and which are

aimed at maximised cost-efficiency especially for

spacecraft;

• Consideration of the operational basis and life-

cycle of the space segment (15-20 years) and

development of resulting strategies for

procurement, storage, reactivation and launch;

• Use of established (ESA) Earth Observation data

archives, with the aim to maximise the availability

of a long term coherent data set;

• Use and extension of existing ground segment

facilities, sharing them with national missions;

• Commonalization of key spacecraft elements where

possible ( e.g. avionics, software, ground segment

interfaces, tools) to minimise costs;

• Minimisation of the schedule to orbit of the first

spacecraft, to avoid (or reduce) data gaps.

1. SENTINEL-1

Sentinel-1 (Fig. 1) is an imaging radar mission in C-

band (5405 MHz) for marine and land monitoring,

aimed at ensuring continuity of data provision for user

services currently available from ERS2/Envisat,

particularly those initiated within the GMES Service

Element programme.

_____________________________________________________

Proc. ‘Envisat Symposium 2007’, Montreux, Switzerland 23–27 April 2007 (ESA SP-636, July 2007)

Figure 1. Sentinel-1 Configuration

To provide guaranteed weather independent day-and-

night revisit time of 6-days globally and 2 days over

Europe and Canada the Sentinel-1 mission is based on

the simultaneous operation of a pair of identical three-

axis stabilised satellites phased by 180 degrees in a

common orbital plane, with a frozen Sun-synchronous

orbit of 693 km mean spherical altitude, a mean local

solar time at ascending node of 18:00 hours, and

14+7/12 revolutions per day.

The operational scenario foresees the development of

the first spacecraft within Segment 1 and the

procurement of an additional spacecraft within Segment

2 (to complete the mission for coverage reasons).

Further spacecraft procurement will be required in later

segments to cover the target operational service period,

currently estimated at 20 years. The mission is tailored

to 95% monthly averaged product availability

(excluding mission loss).

The Sentinel-1 payload consists of a synthetic aperture

radar operating in the C-band with a centre frequency of

5405 MHz. Sentinel-1 has four nominal operational

modes designed for inter-operability with other systems:

- Stripmap Mode (SM) with 80 km swath and

5x5 metre spatial resolution

- Interferometric Wideswath Mode (IW) with

250 km swath, 5x20 meter spatial resolution

and burst synchronisation for interferometry

- Extra-wide Swath Mode (EW) with 400 km

swath and 25x100 meter spatial resolution (3-

Looks)

These modes are available with selectable dual

polarisation (VV+VH, or HH+HV)

- Wave Mode (WV) with 20x20km swath.

Sampled image mode with low data rate and

5x20 meter spatial resolution.

This mode is available with selected single polarisation

(VV or HH)

Tab. 1 shows all measurement modes, with the primary

SAR imaging mode in colour.

Table 1. Sentinel-1 Data Product Characteristics Stripmap

Mode

(SM)

Interfe-

rometric

Wideswath

Mode (IW)

Extra-

wide

Swath

Mode

(EW)

Wave

Mode

(WV)

Swath

Width

80 km 250 km 400 km 20 km x 20

km

Polarisation VV+VH

or

HH+HV

VV+VH or

HH+HV

VV+VH

or

HH+HV

VVor HH

Spatial

Resolution

(Ground

Range

x Azimuth)

5 x 5 m,

single look

5 x 20 m

single look

25 x 100

m 3-

looks

20 x 5

single look

Sensitivity

(Noise

Equivalent

�˚)

-22 dB -22 dB -22 dB -22 dB

Radiometric

Stability

0.5 dB 0.5 dB 0.5 dB 0.5 dB

Radiometric

Accuracy

1.0 dB 1.0 dB 1.0 dB 1.0 dB

Ambiguity

Ratio

(Distributed

Target)

-22 dB -22 dB -22 dB -22 dB

With its greatly improved revisit (Fig. 2), coverage and

timeliness Sentinel-1 is designed for the provision of

guaranteed data services. A single main operational

mode, the Interferometric Wide Swath Mode (IW) is

designed to satisfy most currently known service

requirements thus avoiding conflicts and preserving

revisit performance. This provides robustness and

reliability of service while simplifying mission planning

and facilitating building up a consistent long-term data

archive. The routine operations would normally not be

interrupted but the system is designed to respond to

emergency requests to support disaster management in

crisis situations.

Data delivery to the end user will be within 1 hour from

ground station reception.

Figure 2. Average Revisit of a Satellite Constellation

with 250 km Swath in 12-175 Orbit

Tab. 2 presents an overview of the Sentinel-1 services.

Table 2. Sentinel-1 Services

GMES

Consolidated

Service

Sentinel-1 Contribution

Polar

Environment

Services

- Glacier and Snow

Monitoring

- Iceberg Monitoring

- Sea Ice Monitoring

- Oil Discharge

Monitoring

- Near Shore Ice

Complex

- Land Monitoring

- Lake Ice Monitoring

- River Ice Monitoring

Marine &

Coastal

Environment

Sea surface winds, currents & waves

Oil spill information services (surveillance,

drift forecasting)

Ship detection services for fisheries and

security

Land

Information

Services

Basic Land Cover

Soil Sealing Map

Forest

Monitoring

Services

Green house gas reporting

Sub-National Forest Information Updates

Mapping and Monitoring of Disturbances

(Clearing, Fires)

Land Cover & Forest Indicators

Geo-hazard

Risk

Management

Historical measurements of ground motion:

subsidence risk

Subsidence and landslide monitoring

(tunnelling project, water table change)

Geological engineering

Flood and

Fire Risk

Operational

Information

Services

Flash flood early warning

Floods rapid mapping

Flood risk analysis

Food Security

Information

Mapping ploughing time and acreage

Mapping planting time and acreage

Mapping cultivated area at harvest/during

growing period

Humanitarian Rapid mapping for out-of-area crises

Aid

operation

Cartography for development and

reconstruction planning

Key features of Sentinel-1:

- Mass 2.1 tons

- Power 5 kW

- Antenna size 10m x 1.4m

- Radar freq. 5405 Mhz

- Data Storage 2TB

- Downlink rate about 500 Mbps

- Near-polar sun synchronous orbit, 12-day repeat cycle

- 06:00 Local Time Descending Node (dawn-dusk)

- Launcher class Soyuz

2. SENTINEL-2

Sentinel-2 is a multispectral imaging mission. Its main

purpose is the continuity of Landsat, SPOT &

Vegetation-type data and the continuity to services for

multi-spectral high-resolution optical observations over

global terrestrial surfaces.

The Sentinel-2 mission (Fig. 3) is based on the

simultaneous operation of two identical satellites phased

by 180 deg. in a common orbital plane in a frozen sun-

synchronous orbit.

Figure 3. Sentinel-2 Configuration

resulting from Phase A/B1

The Sentinel-2 Multi Spectral Instrument (MSI) uses the

push-broom concept with an instantaneous swath width

of 285 km. The instrument features 13 Infrared bands,

10 in the Very Near Infrared (VNIR) and 3 in Short-

wave Infrared (SWIR). Resolution is 20 m in general,

except 60 m for atmospheric correction channels, and

10 m for 4 bands. Fig. 4 shows the spectral bands along

with their respective resolution.

Figure 4. 13 Spectral bands versus

spatial sampling distance

A possible optical configuration for the MSI is shown in

Fig. 5. This is the result of a definition study; the

detailed design has to be selected. The VNIR focal

plane technology will be CMOS or CCD, while for the

SWIR focal plane cooled MCT (Mercury Cadmium

Telluride) detectors (hybridised on CMOS read-out

circuit) will be used.

Figure 5. Possible MSI Overall Configuration

The baseline data acquisition scenario is based on the

permanent utilisation of 2 to 4 ground, with a data

downlink bit rate of 3x150 Mbps during overpass, and

an internal mass memory of 2 Terabits. A Real Time

transmission capability allowing direct data downlink is

also available. The downlink sub-system is a candidate

for commonalization with other Sentinels.

The services provided by Sentinel-2 are shown in the

following Tab. 3.


GMES Initial

Service

Sentinel-2 Features

Global

Change -

Land

Mapping services for monitoring urban areas

in Europe (urban sprawl, urban planning

modelling & forecasting, changes in urban

land use, environmental monitoring and

enforcement of urban planning discipline

Land cover & Comprehensive information services for

Land use

change

European users with respect to mainly

European policies (Water, Soil, Integrated

Coastal Zone Management, Urban

Environment, Spatial Development)

Monitoring

Forest area / forest area change map

Forest type map

Forest fragmentation

Food Security

early warning

Support to Crop and Food Supply Assessment

Agricultural mapping

Crop Yield assessment

Humanitarian

Aid

Appropriate and reliable application of

geographic information for humanitarian

organisations

Risk

Management

(flood and

fires)

Monitoring of floods, forest fires, volcano

eruptions, subsidence and landslides

Sentinel-2 will provide a large quantity of data, about 6

Terabits of data per day for each satellite. A significant

proportion of these data are however expected to be

cloud-covered, so that an efficient cloud screening is

required before disseminating data from the PDGS to

the service segment.

The satellite is designed to be largely autonomous and

simple to operate: continuous imaging mode over land,

with a period of 2 weeks without reprogramming need

under nominal operations, and acquisition of

housekeeping and science data telemetry over each

ground station pass. Similarly as for Sentinel-1, access

to the satellite is protected by telecommand

authentication, (partial) housekeeping telemetry

encryption and payload data downlinks are encrypted.


- Mass 1000 kg

- Power 1175 W (GaAs Triple

Junction Cells, Li-Ion

Battery)

- Data Storage 2TB : lossy compression (wavelet

technology)

- Downlink rate about 450 Mbps (X-band)

- Near-polar sun synchronous orbit

- 10:30 Local Time Descending Node

- Launcher class: Vega

3. SENTINEL-3

Sentinel-3 implements 4 core operational missions in

continuity of existing ones, delivering:

- Sea surface topography (SSH) and, significant

wave height (SWH) over the global ocean to an

accuracy and precision exceeding that of Envisat

RA-2.

- Sea and Land surface temperature (SST, LST), at

least at the level of quality of the Advanced Along-

Track Scanning Radiometer (AATSR) instrument

- Visible and Infrared radiances (“Ocean Colour”)

for oceanic and coastal waters, determined to an

equivalent level of accuracy and precision as

MEdium Resolution Imaging Spectrometer

(MERIS) instrument data with complete Earth

coverage in 2 to 3 days, and co-registered with SST

measurements.

- Visible, Near Infrared, Short-Wave Infrared, and

Thermal Infrared radiances (“Land Colour”) for

land surface, with complete Earth coverage in 1 to

2 days, with products equivalent to those derived

from MERIS, A/ATSR and Spot VGT, together

with those from their combination.

The Sentinel-3 mission is based on a medium-size 3-

axis stabilised satellite flying in a sun- synchronous

frozen orbit at 799.8 km altitude, corresponding to 14 +

7/27 orbital periods per day. The orbit repeat period is

therefore 27 days, as required for sea surface

topography sampling. However, the altitude is close to

that of a 4 days short-repeat orbit such that, considering

the wide swath of the optical instruments, the optical

observations can achieve the desired rapid global

coverage. The local time at descending node (LTDN)

will be 10:00 to 10:30, which is the best compromise

between the constraints of the ocean and land colour

observations and those of continuity for the sea surface

temperature observations.

Figure 6. Sentinel-3 Configuration resulting

from Phase A/B1

In trade offs between instrument complexity and

development risk, and considering the robustness

required for an operational system, it has been

determined that the Sentinel-3 mission is best fulfilled

by a constellation of two satellites.

The payload complement of Sentinel-2 fulfils two tasks:

The Topography Mission with

- Bi-frequency Synthetic Aperture Radar Altimeter

(Fig. 7)

Heritage from CryoSat (SIRAL) and Jason, using

the Ku- (13.575 GHz) and C-band (5.41 GHz, for

ionospheric correction in a 320 MHz bandwidth),

with an antenna reflector of 1.2 m diameter. New

features are a SAR mode (along-track SAR

operation with a nadir resolution of ca 300m) and

open-loop tracking, resulting in an improved

monitoring of coastal ocean, ice surfaces and in-

land water.

- Microwave Water Vapour Radiometer (Fig. 8)

Derived from the similar instrument on Envisat,

with several technological updates and features:

o two frequency operation at 23.8 and 36.5

GHz (a 3-frequency concept with 18.7

Ghz is also under evaluation)

o Dicke-type radiometer with internal

calibration (hot load, sky horn)

o Antenna reflector of 0.6 to 0.8 m diameter,

depending on the concept

- Precise Orbit Determination (POD) including

o GNSS (GPS and Galileo) Receiver with 2

cm radial accuracy

o Laser Retro-Reflector

Figure 7. Radar Altimeter Configuration

Figure 8. Microwave Radiometer Overview

The Optical Payload consists of

- Ocean and Land Colour Instrument (OLCI) with

strong heritage from MERIS (Fig. 9) is a

pushbroom-type imaging instrument featuring 5

cameras, arranged cross-track, with a de-pointing of

19o to minimise the sun-glint effect. It observes in

15 bands in the visible/NIR, very similar to the

MERIS bands. The OLCI uses no mechanisms,

except for calibration purposes. The OLCI spatial

resolution at the sub-satellite point is < 300 m, with

an instantaneous swath of 1120 km.. The required

spatial resolution of < 0.3 km at the sub-satellite

point is met; the swath covers the Earth surface in

less than 3 days for the ocean and near 1 day for

land (based on the two satellite constellation).

The Resolution is optimized for observation with

full resolution over Coastal/Land (300 m ), reduced

for the open ocean (1.2 km).

Figure 9. OLCI Camera Arrangement

The Sea and Land Surface Temperature (SLST)

instrument (with strong heritage from AATSR) is a

dual-conical scanning imager operating in the

Visible and Infrared down to TIR and featuring the

following key characteristics:

Dual-view (along-track) in order to

provide the highest quality atmospheric

correction 3 bands;

Continuous day-night operation;

Accurate two-point radiometric calibration

to maintain the long-term accuracy of

AATSR;

One IR channel used for co-registration

with OLCI

- The baseline SLST design (see Fig. 10) is based on

a dual scanning mechanism with dichroic

separation of the beams and a common focal plane

cooled to 65 K. Two blackbodies provide for

accurate calibration.

Figure 10. SLST instrument

The rotation of the two scanners, both with 150 ms

period results in two scan lines defining the dual-

view and single-view swaths, which, for the

selected orbit, are 1675 km and 750 km wide,

respectively.

The OLCI and SLST have overlapping swaths, whose

observations in the common swath are co-registered to

0.1 pixel RMS. This is facilitated by the two

instruments being mounted on a common base plate,

also supporting the star sensors for improved geo-

location (Fig. 11).

Figure 11. Overlapping Swath of OLCI and SLST

Tab. 4 presents the Sentinel-3 Services.


GMES Initial Service Sentinel-3 Features

Marine and Coastal

Environment

Sea-surface topography

Mesoscale circulation

Water quality

Sea-surface temperature

Wave height and wind

Sediment load and transport

Eutrophication

Polar Environment

monitoring

Sea-ice thickness

Ice surface temperature

Marine Security Ocean-current forecasting

Water transparency

Wind and wave height

Global Change - Ocean Global sea-level rise

Global ocean warming

Ocean CO2 flux

Global Change - Land Forest cover change mapping

Soil degradation mapping

Land cover & Land

use change

Land use mapping

Vegetation indices

Forest Monitoring Forest cover mapping

Food Security early

warning

Regional land-cover mapping

Drought monitoring

Humanitarian Aid Land use mapping

Air Pollution (local to

regional scales)

Aerosol concentration

Risk Management

(flood and fires)

Burned scar mapping

Fire detection


- Mass 1270 kg

- Power 1100 W

- Data Storage 2TB : lossy compression (wavelet

technology)

- Downlink rate about 300 Mbps

- Near-polar frozen sun synchronous orbit

- 14 +7/27 rev/day (10:00 - 10:30 LTDN)

- Launcher class: Vega

4. STATUS OF SENTINEL-1, -2 AND -3

For all three Sentinels the early development phases A

and B1 are now concluded. Sentinel-1 has finalized the

tender evaluation procedure for the follow-on phases up

to commissioning and has selected the industrial

consortium for the future tasks. The industrial activities

are starting now.

Sentinel-2 and -3 currently are expecting the industrial

proposals for the next phases, to be followed by the

tender evaluation process. The foreseen start of the next

phase for both of them is October 2007.

Major key data for the Sentinel satellites are:

- Preliminary Design Review

o S-1 February 2008

o S-2 October 2008

o S-3 August 2008

- Critical Design Review

o S-1 March 2009

o S-2 Mid 2010

o S-3 February 2010

- Launch

o S-1 November 2011

o S-2 April 2012

o S-3 August 2012

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