APEX – Airborne Prism Experiment Dispersive Pushbroom Imaging Spectrometer for Environmental Monitoring

Michael E. Schaepmana,b, Klaus I. Ittena and The APEX Teamc

a Remote Sensing Laboratories, Dept. of Geography

University of Zurich, Winterthurerstrasse 190, CH - 8057 Zurich

b Wageningen UR, Centre for Geo-Information NL - 6700 AA Wageningen

c The APEX Team: Jens Nieke, Daniel Schläpfer, Johannes W. Kaiser, Jason Brazile

(RSL), Walter Debruyn, Koen Meuleman (VITO), Andreas Neukom, Hans Feusi, Peter Adolph, Renzo Moser, Thomas Schilliger (HTS AG), Lieve De Vos, Nico van Vooren

(OIP), Peter Kohler, Markus Meng, Jens Piesbergen (Netcetera AG), Peter Strobl (DLR), Jose Gavira, Gerd Ulbrich, and Roland Meynart (ESA)

Keywords: Imaging spectrometer; hyperspectral; pushbroom; calibration; validation; sensor design; data processing; imaging spectroscopy applications Over the past few years, a joint Swiss/Belgium ESA initiative resulted in a project to build a precursor mission of future spaceborne imaging spectrometers, namely APEX (Airborne Prism Experiment). APEX is designed to be an airborne dispersive pushbroom imaging spectrometer operating in the solar reflected wavelength range between 400 and 2500 nm. The system is optimized for land applications including limnology, snow, and soil, amongst others. The instrument is optimized with various steps taken to allow for absolute calibrated radiance measurements. This includes the use of a pre- and post-data acquisition internal calibration facility as well as a laboratory calibration and a performance model serving as a stable reference. The instrument is currently in its breadboarding phase, including some new results with respect to detector development and design optimization for imaging spectrometers. In the same APEX framework, a complete processing and archiving facility (PAF) is developed. The PAF not only includes imaging spectrometer data processing up to physical units, but also geometric and atmospheric correction for each scene, as well as calibration data input. The PAF software includes an Internet based web-server and provides interfaces to data users as well as instrument operators and programmers. The software design, the tools and its life cycle are discussed as well.

APEX – Airborne Prism ExperimentDispersive Pushbroom Imaging Spectrometer

for Environmental Monitoring

Michael E. Schaepmana,b, Klaus I. Ittena and The APEX Teamc

a Remote Sensing Laboratories, Dept. of GeographyUniversity of Zurich, Winterthurerstrasse 190, CH - 8057 Zurich

b Wageningen UR, Centre for Geo-InformationNL - 6700 AA Wageningen

c The APEX Team: Jens Nieke, Daniel Schläpfer, Johannes W. Kaiser, Jason Brazile (RSL), Walter Debruyn, Koen Meuleman (VITO), Andreas Neukom, Hans Feusi, Peter Adolph,

Renzo Moser, Thomas Schilliger (HTS AG), Lieve De Vos, Nico van Vooren (OIP), Peter Kohler, Markus Meng, Jens Piesbergen (Netcetera AG), Peter Strobl (DLR), Jose Gavira,

Gerd Ulbrich, and Roland Meynart (ESA)

Outline of the Talk

Scope of APEX

Organization and Timeline

Selected Specifications

Components and Breadboarding Activities

Conclusions

Scope of APEX

APEX is an airborne simulator for the support and development of future space borne systems for the study of land surface processes.

APEX will be able to• Simulate,• Calibrate, and• Validate

the planned ESA imaging spectrometer missions.

APEX will foster the use of imaging spectrometer data in Europe and will support the application development for imaging spectroscopy products.

APEX is currently an important perspective of an imaging spectrometer covering the solar reflected range between 400-2500 nm at high spectral resolution.

APEX is a joint Swiss/Belgian ESA PRODEX project and will complemented by other European initiatives, such as ARES (GFZ, DLR Germany)

APEX Organization

ESA Team

Instrument Manager &Detector Development

Gerd Ulbrich &Roland Meynart

PRODEXTechnical OfficerJosé Gavira Izquierdo

Contracts OfficerUlrich Sterzl

Principal InvestigatorKlaus Itten

Science Team

Project ManagerJens Nieke

PAF ScientistDaniel Schläpfer

Processing ScientistJohannes Kaiser

Computer ScientistJason Brazile

Operations Team

Co-InvestigatorWalter Debruyn

Instrument OperationsKoen Meuleman

Processing OperationsPieter Kempeneers

Flight OperationsBart Deronde

Industrial Team

Industrial PrimeHTS AG

Optical SubsystemOIP Sensor Systems

Electronic SubsystemNetcetera AG

SWIR DetectorsSofradir

Calibration Home BaseDLR

Project ScientistMichael Schaepman

APEX Timeline

20052004200320022001< 2000

Institutes Phase C/D

APEX Studies

Phase E(5+5 years)

APEX ITT1

APEX ITT2

Industry Phase C/D

BDR

KOM

PDR

Acceptance

DeliveryCalibration Home Base

SWIR Detector

Today

CDR

VNIR Detector

ITT = Invitation to TenderKOM = Kick-Off Meeting, BDR = Baseline Design ReviewPDR = Preliminary Design Review, CDR = Critical Design Review

Construction

Integration

APEX Selected SpecificationsNarrow field of view FOV 28° deg

IFOV 0.49 mrad (spatial resolution across slit), approx. 1000 pixels across track

Optimal adjustment to aircraft operation Frame rate and integration time independently variable, synchronized, and = 43.3 Hz

Operating altitudes between 3-10 km above Sea level

Total spectral pixels on chip Prior to binning 312 (VNIR) + 195 (SWIR)

Total spectral bands Supported by the electronics = 300, resulting in a spectral sampling interval (and width) of = 5 (10) nm in VNIR and = 10 nm in SWIRReprogrammable on-chip binning of spectral bands (using software upload)

Schematic APEX Components

ASSY 1 ASSY 2 ASSY 3

Thermal Enclosure

STP (Stabilised Platform)

OCI (Operator Cockpit /

Pilot Interface)

NSS (Navigational Subsystem)

OMU (Opto-Mechanical

Unit)

STPA - IF (Platform and

Aircraft Interface)

APEX - INSTRUMENTAirborne

Pilot ScreenInertial

Unit Data Harness Power Harness

GPS Antenna

Fixation

Data Flow

Operator Screen

FMS (Flight Manage-

ment System)

Electronic Rack

CSU (Control and Data

Storage Unit)

Assembly of the Opto-Mechanical Unit (OMU)

APEX SWIR Detector: Pre-Engineering ModelDetector material HgCdTe (‘MCT’) detector array - hybridised on a CMOS multiplexerSize 1000 x 256 square pixels, 30 um pitchFeatures Addressable readout, fast operation, integrated in cryostat cooler

assemblyWavelength range 940 – 2500 nmQuantum efficiency >55 % averageOperating temperature 130-165 K

DewarCooler

Entrance window

Focal Plane Assembly Breadboard

APEX SWIR Detector: Pre-Engineering Model II

The picture shows dewar assembly (left) and the compressor (right). On top of the dewar is the rectangular sapphire window located. The black rectangle under the window is the cold stop aperture. The bright yellow area below is reflected light from the shiny surface of the dewar hood. The dewar includes a 1st generation IRFPA. The metal connecting piece between the compressor and the detector housing is part of the transport tool.

APEX Optical Subunit (OSU) DrawingThe Optical Subunit (OSU) is fully mounted on the stabilizing paltform, during operation in an aircraft

Transparent grey: cover for the optical base plate, electronics, and calibration

Purple: Optical Base Plate with all relevant optical parts mounted on it

Dark green: mass to balance center of gravity

Dispersive Pushbroom Spectrometer Design

SWIR-VNIR prism

VNIR prism

SWIR Detector Lens

VNIR Detector Lens

VNIR detector

Collimator

Ground imager

SWIR detector

Inflight Calibration Installation

APEX: Other Breadbording Activities

Left: Visible/Nearinfrared detector as provided by E2VMiddle: Heat pipe for cooling of heat exhibiting OSU parts (e.g., calibration

lamp)Right: Inertial Measurement Unit (IMU) as part of the Applanix Inertial

Navigation System (for sensor/aircraft attitude recording)

APEX Electronic: Data Streams Overview

APEX Electronic Setup and Block Diagram

APEX Electronics: Breadboarding

Top left: Prototype of PCI boadTop right: Schematic drawing of PCI board

Left: Ruddedized harddisk (one of six)

APEX: Functional Blocks of the Software Architecture

APEX PAF: The Processor Foundation

PAF Hardware: Linux Cluster,PAF Hardware: Linux Cluster,Archiving SystemArchiving System

PAF API: IDLPAF API: IDL--emacsemacs, XML, XML--tools,tools,CVS, TCL/CVS, TCL/webshwebsh

PAF Processor: PAF Processor: IDL, XML, CIDL, XML, C

APEX PAF

SearchAPEX

Archive

Server

Core

Web

Processor

Input

ToolsProcessing

ToolsCollaboration

ToolsBrowsing

Docs

Co-Developers

Users

Operators

CHB Data

Conclusions

APEX is currently just before the Critical Design Review (CDR) meeting, scheduled for this year (December)

Many technical solutions have been adapted to reflect the latest standards of technology and scientific knowledge (stability of temperature, in-flight calibration, etc.)

Selected breadboarding activities are already in place and critical items are assessed

First data for the scientific user community shall be available in 2005!