An Advanced High Resolution Optical Sensor for Small Satellite Mapping Missions

AN ADVANCED HIGH RESOLUTION OPTICAL SENSOR FOR SMALL SATELLITE MAPPING MISSIONS

David Purl, Mike Cutter Alex da Silva Curiel Dr Wei Sun Sir Martin Sweeting

©SSTL Contents

• Overview of Beijing-1 project – Mission –Instrument – Next generation instrument

• Mission status –Applications

©SSTL 2 Advancing smallsat capability

• World-leading performance in small satellites – Best GSD achieved for the size spacecraft – Lowest cost spacecraft to achieve this GSD • Beijing-1

Mission Launch GSD Mass 6 QuickBird-2 2002 0.61 980 IKONOS-1 2000 1 726 ORBVIEW-4 2002 1 368 5 IGS-1a 2003 1 850 ORBVIEW-3 2004 1 300 KOMPSAT-2 2005 1 470 4 Beijing-1 EROS-A 2001 1.8 280

EROS-B 2006 1.8 280 ) TOPSAT m

Formosat-2 2004 2 764 (

D 3 SPOT-5 2002 2.5 3030

IRS-P5 (Cartosat) 2004 2.5 1500 GS TOPSAT - SSTL 2006 2.85 112 ALOS 2006 2.5 4000 2 RazakSat-1 2007 2.5 200 Earlybird 1998 3 310 OFEQ-5 2002 3 300 1 Beijing-1 - SSTL 2006 4 168 Lewis 1998 5 288 PROBA-1 2002 5 120 0 0 500 1000 1500 Mass (kg)

©SSTL 3 Constellations for EO

• Existing EO satellites provide100 – High spatial resolution s) ay d

– Good spectral discrimination ( Traditional Earth d Resources Missions •But… 10 – Poor temporal resolution Revisit perio

– Very high cost Constellations Commercial Remote sensing 1 • Small Satellites SSTL Constellations – Very low unit cost of small satellites – Constellations of EO satellites become affordable – Capable of medium spatial 0.1 resolution and spectral 0.1 1 10 100 discrimination Spatial resolution (metres)

©SSTL 4 Beijing-1 project

• Procurement by Beijing Land View Imaging Information Technology Company Ltd, and the Chinese Ministry of Science and Technology – US$18m contract (Development, Space segment, Ground segment, Launch and LEOP)

• Mission – Systematic mapping of China over a 5 year period • Including Olympics preparation – Participate in Disaster Monitoring Constellation (DMC)

©SSTL Jul03 – contract start Launch - Oct055 Beijing-1 mission

• Specifications – Up to 15 minute of continuous mapping operations per orbit • 4m Panchromatic data acquisition •Data downlinking

– Operate as part of Disaster Monitoring Constellation • 32m multispectral

©SSTL 6 Beijing-1 Platform

• 166kg, Enhanced SSTL microsatellite

• Dual redundant avionics

• 5 year design life

• S-band TM/TC

•Power – Body mounted arrays, triple junction GaAs – 50W OAP generated

•Data Handling – Flexible Control and Updating of On-Board Software from the Ground Station

• High performance ADCS – Stable and Flexible Attitude Control for Off-Pointing Imaging – Off-nadir pointing • ±30º Roll – Control 0.1 º (3-σ), stability 2.5mdeg/s

• Orbit control and determination –GPS navigation – Xenon electro-thermal propulsion, 17m/s – Maintenance in constellation with DMC

©SSTL 7 Payload

• High resolution payload – 4-metre GSD pan (SIRA Ltd) – 24km swath width 3,000km swath length – 40Mbps X-band downlink – On-board data compression – 3 Gbytes solid-state storage – 240 Gbytes hard disk storage system

• DMC payload – 32-metre GSD multi-spectral (3-bands) – >600km swath width – 8Mbps S-band downlink – 1.5Gbytes Solid State Storage

©SSTL 8 Payload block diagram

SSDR Solid State Data Recorder NV-DR Non-Volatile Data Recorder MS IMGR PAN DSP RTR Digital Signal Processor / Router PAN Panchromatic imager MS IMGR Multispectral imager OBC386 On Board Computer NV-DR DSP RTR DSP RTR NV-DR RF Receivers

2x CAN

OBC386 OBC386 SSDR SSDR SSDR SSDR 512Mb 512Mb 1Gb 2Gb

RF Transmitters RF Transmitters

S-band X-band D/L D/L

20, 40Mbps

©SSTL 8Mbps 9 Payload Support

• Image processor and compressor –DSP based – Software defined JPEG compression

• Solid State Data Recorders – PowerPC based with SRAM technology

• Hard drive data recorders – Flexible Use of Hard Disk for On Board Data Storage, to Get More Storage Space with Lower Cost and Lower Power Consumption – 240GByte

• X-band downlink – 20+40Mbps – Flexible Downlink Mode for the Ground Station: •Real Time Mode • Store and Forward Mode

©SSTL 10 Mapping instrument

• Panchromatic imager – Supplied by SIRA (acquired by SSTL in March 2006)

– Sensor CCD Pushbroom, 8 micro pixels – Focal length 1.37m

– Band 500-800nm – GSD 4m (@686km) – Swath 24km – Aperture 310mm ©SSTL 11 Mapping instrument

• Compact, on-axis telescope, scalable design –GSD – Area on focal plane –No requirement for satellite motion compensation – Unlimited “on-time”

• Low coefficient of thermal expansion providing good stability – Pseudo-Isostatic mount – Carbon fibre composite structure – Zerodur and fused silica optics – Invar optical mounts

• Robust optical design – In-orbit adjustable focusing – Compatible with high vibration levels – Thermally isolated from platform

©SSTL 12 Imaging Payload Description

• Overview – Digitisation 10 bits – SNR 140 (35º latitude and albedo of 0.3)

– Mass 25kg – Power 12W – Volume 780x380x380mm

©SSTL 13 Performance achieved

Parameter Required Achieved System MTF (Ground) GSD (m) 4 4 MTF, cross-track, 1° field Nyquist Swath (km) 24 24 1 0.8 Band (nm) 500-800 500-800 0.6 Band edge accuracy across FoV ±30 2 F (nm) MT 0.4 0.2 Energy in pass-band ≥ 90% 98% 0 MTF at Nyquist: Centre ≥ 15% ≥ 19.6% 0 102030405060 Edge ≥ 10% ≥ 13.6% Cycles/mm Signal-to-noise ratio ≥ 140 210 MTF, along-track, 1° field 1 Power (W) at 28V ≤ 25 24 0.8 Mass (kg) ≤ 12 11.9 0.6 3 Volume (mm ) except mounting 790x400x400 790x380x378 MTF 0.4 feet 0.2

0 0 102030405060 Cycles/mm Parameter Conditions Spectral response Orbit 686 km, sun synchronous,11:00 1.8E+05

LTAN, nadir pointing 1 1.6E+05 sr^- . Signal 0.3 albedo at 35° latitudeat 11:00 on 2 1.4E+05 ^-

m 1.2E+05 March 21st c .

W 1.0E+05 Temperatures at imager mounting panel:10°C ± 10° 8.0E+04 DU /

± 10° uncertainty-25°C to +60°C- A , 6.0E+04 e

50°C to +88°C s n

o 4.0E+04 s p Vibration (qual) 21 grms random vibration 2.0E+04 Re 1 g2/Hz peak 0.0E+00 450 500 550 600 650 700 750 800 850 ©SSTL Wavelength, nm 14 Next generation payload

Parameter Performance

Bands Panchromatic Multi-spectral: 4-5 bands (R,[RE],G,B,NIR) Panchromatic GSD 2.5m

Multi-spectral GSD 5.0m

Imaging ground swath widths 20km PAN and 20km MS (700km)

Modulation transfer function (MTF) Centre: >= 13% Nyquist, >=26% half Nyquist, Edge: >= 9% Nyquist, >=18% half Nyquist Signal to Noise Ratio (SNR) Panchromatic: 103 (2.5m GSD)

Signal to Noise Ratio (SNR) Blue: 64 Green: 90 (5m GSD) Red: 70 Near Infra-Red: 100

©SSTL 15 Launch

•Oct’05

©SSTL 16 Results from an operational mission

Products and applications

©SSTL Data Products of Beijing-1

Level Descriptions File Format L1 Radiometric Correction RAW

L2 Systematic Geometric Correction GeoTIFF

L3 Precision Geometric Correction using GCPs GeoTIFF

L4 Ortho-Rectification using DEM Data GeoTIFF

L5 3D View Image Product using DEM data -

L6 Fusion Image Product using 32m Multi- GeoTIFF Spectral Image and 4m Panchromatic Image

Image Data before De-stripping Image Data after De-stripping

Strip Noise is Removed using Statistical Method and Wavelet Method

Image Data before Image Data after Radiometric Correction Radiometric Correction

Radiometric Correction of MSI includes Automatic Band Registration and ©SSTL MTF Restoration using Wiener Filter 20 Examples of data products (L2product: Systematic Geometric correction for MSI)

L1: Radiometric Correction Product L2: Systematical Geometric Correction Product

(1) Imaging in Ascend (2) Average Accuracy of Systematical Geometric Correction is 600 meters.

L3 Product + DEM Data L4: Ortho-Rectification Product

(1) Average Accuracy is within 1 Pixel in Plain Areas (2) Average Accuracy is between 1 and 2 Pixels in Mountain Areas ©SSTL 22 Examples of data products (L3 product: Precision geometric correction for MSI)

L2 Product＋GCPs L3: Precision Geometric Correction Product

(1) Average Geometric Accuracy is within 1 pixel in Plain Areas (2) Average Geometric Accuracy is between 2 and 3 pixels in Mountain Areas

• Land Use / Land Cover Analysis

• Environmental Monitoring

• Precision Agriculture

• Urban Dynamic Monitoring

• Disaster Monitoring

• Comprehensive Regional Management System

• Small satellite EO capability now includes high resolution imaging

• Beijing-1 operational – Commercial service provider – Excellent results, products and applications

• Scalable, Robust Instrument design – Matched to microsat environment – 1-5m GSD (Pan) – 2-20m GSD (MS)