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A Cloud Profiling Radar (CPR), an Atmospheric LIDAR (ATLID), a Broadband Radiometer (BBR) and a Multi- Spectral Imager (MSI) constitute the payload complement of the EarthCARE satellite. The four instruments will provide synergistic data on cloud and aerosol vertical structure, horizontal cloud structure and radiant flux from sub-satellite cells. By acquiring images of the clouds and aerosol distribution, the MSI instrument will provide important contextual information in support of the radar and LIDAR data processing.
The MSI instrument itself consists of two camera units, the Thermal Infrared (TIR) camera and the Visible, Near- Infrared and Shortwave Infrared (VNS) camera, that are readout through a shared Front-End-Electronics (FEE) unit, all controlled by the Instrument Control unit (ICU).
The subject of this paper is the characterisation and performance verification results of the TNO designed and built Proto Flight Model (PFM) VNS camera in conjunction with the SSTL designed and built PFM FEE unit. This paper presents an overview of the characterisation and performance verification philosophy, followed by a more detailed presentation of several important measurements sets highlighted below.
Optical quality measurements (Modulation Transfer Function)
In order to measure the MTF of the VNS camera for several spatial frequencies simultaneously, a dedicated laboratory setup was built that provided the camera with block illumination patterns. Using Fourier analysis these optical block functions could be separated into their higher order components, resulting in acquisition of the MTF performance for several spatial frequencies concurrently.
Spectral Response measurements
For the VNS camera the spectral response was measured from 300nm up to 2400nm over the entire instrument swath of 360pixels. In order to perform this in an efficient manner a lock-in amplification setup was devised that included a “high” power pulsed tunable laser source, integrating spheres and monitoring detector.
In order to control pulse to pulse variations of the laser source and have a correct background correction, the 1kHz pulse frequency of the laser was further modulated by a several Hz chopper, resulting in spectral measurements with ~1% accuracy.
Straylight measurements
The straylight requirements for the VNS camera were specified as the maximum allowable amount of signal in an infinite dark area when illuminating the VNS camera with semi- infinite light source in an adjacent area. A dedicated tool was developed to simulate these (semi) infinite areas.
Radiometric characterization
For the VNS camera the required absolute radiometric accuracy was quite relaxed, 10% (5% goal). However, the interchannel radiometric accuracy between the VNS channels is required to be better than 1%. This last requirement could not be achieved by “standard” radiometric calibration methods and a calibration method was developed using the VNS camera itself in collaboration with an integrating sphere that was used in radiance and irradiance modes.After finalisation of the performance testing and calibration measurements the VNS camera was delivered to SSTL mid 2017 for further integration on the MSI Optical Bench Module and alignment with the TIR camera and other MSI subsystems by SSTL.
In December 2002, ESA granted Alcatel Space with a phase A study of the EarthCARE mission in which Alcatel Space is also in charge to define ATLID.
The primary objective of ATLID at the horizon 2011 is to provide global observation of clouds in synergy with a cloud profiling radar (CPR) mounted on the same platform. The planned spaceborne mission also embarks an imager and a radiometer and shall fly for 3 years.
The lidar design is based on a novel concept that maximises the scientific return and fosters a cost-effective approach. This improved capability results from a better understanding of the way optical characteristics of aerosol and clouds affect the performance budget.
For that purpose, an end to end performance model has been developed utilising a versatile data retrieval method suitable for new and more conventional approaches. A synthesis of the achievable performance will be presented to illustrate the potential of the system together with a description of the design.
This paper presents the design and performance of the ATLID instrument, and relates the main development issues. The technical challenges and the main innovations are highlighted.
Spaceborne lidar systems have been the subject of extensive investigations by the European Space Agency since mid 1970’s, resulting in mission and instrument concepts, such as ATLID, the cloud backscatter lidar payload of the EarthCARE mission, ALADIN, the Doppler wind lidar of the Atmospheric Dynamics Mission (ADM) and more recently a water vapour Differential Absorption Lidar considered for the WALES mission. These studies have shown the basic scientific and technical feasibility of spaceborne lidars, but they have also demonstrated their complexity from the instrument viewpoint. As a result, the Agency undertook technology development in order to strengthen the instrument maturity. This is the case for ATLID, which benefited from a decade of technology development and supporting studies and is now studied in the frame of the EarthCARE mission. ALADIN, a Direct Detection Doppler Wind Lidar operating in the Ultra -Violet, will be the 1st European lidar to fly in 2007 as payload of the Earth Explorer Core Mission ADM. WALES currently studied at the level of a phase A, is based upon a lidar operating at 4 wavelengths in near infrared and aims to profile the water vapour in the lower part of the atmosphere with high accuracy and low bias. Lastly, the European Space Agency is extending the lidar instrument field for Earth Observation by initiating feasibility studies of a spaceborne concept to monitor atmospheric CO2 and other greenhouse gases.
The purpose of this paper is to present the instruments concept and related technology/instrument developments that are currently running at the European Space Agency. The paper will also outline the development planning proposed for future lidar systems.
The purpose of the paper is to present the progress in the instrument and subsystem design. The instrument is currently in phase C where the detailed design of all sub-systems is being performed. Emphasis will be put on the major technological developments, in particular the laser Transmitter, the optical units and detector developments.
The satellite will be placed in a Sun-Synchronous Orbit at about 400 Km altitude and14h00 mean local solar time. The payload consisting of a High Spectral Resolution UV Atmospheric LIDar (ATLID), a 94GHz Cloud Profiling Radar (CPR) with Doppler capability, a Multi-Spectral Imager (MSI) and a Broad-Band Radiometer will provide information on cloud and aerosol vertical structure of the atmosphere along the satellite track as well as information about the horizontal structures of clouds and radiant flux from sub-satellite cells.
The presentation will cover the configuration of the satellite with its four instruments, the mission implementation approach, an overview of the ground segment and the overall mission development status.
End-to-end performance analysis using engineering confidence models and a ground processor prototype
The EarthCARE Multispectral Imager (MSI) is relatively compact for a space borne imager. As a consequence, the immediate point-spread function (PSF) of the instrument will be mainly determined by the diffraction caused by the relatively small optical aperture. In order to still achieve a high contrast image, de-convolution processing is applied to remove the impact of diffraction on the PSF. A Lucy-Richardson algorithm has been chosen for this purpose.
This paper will describe the system setup and the necessary data pre-processing and post-processing steps applied in order to compare the end-to-end image quality with the L1b performance required by the science community.
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