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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.
One activity has centred on the use of coated, silicon wafers, patterned with ribs, that are integrated onto a mandrel whose form has been polished to the required shape. The wafers follow the shape precisely, forming pore sizes in the sub-mm region. Individual stacks of mirrors can be manufactured without risk to, or dependency on, each other and aligned in a structure from which they can also be removed without hazard. A breadboard is currently being built to demonstrate this technology.
A second activity centres on glass pore optics. However an adaptation of micro channel plate technology to form square pores has resulted in a monolithic material that can be slumped into an optic form. Alignment and coating of two such plates produces an x-ray focusing optic. A breadboard 20cm aperture optic is currently being built.
Silicon Pore Optics are made of commercial Si wafers using process technology adapted from the semiconductor industry. We present the manufacturing process ranging from single mirror plates towards complete focusing mirror modules mounted in flight configuration. The performance of the mirror modules is tested using X-ray pencil beams or full X-ray illumination. In 2009, an angular resolution of 9 arcsec was achieved, demonstrating the improvement of the technology compared to 17 arcsec in 2007. Further development activities of Silicon Pore Optics concentrate on ruggedizing the mounting system and performing environmental tests, integrating baffles into the mirror modules and assessing the mass production.
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.
Silicon Pore Optics is an enabling technology for future L- and M-class astrophysics X-ray missions, which require high angular resolution (~5 arc seconds) and large effective area (1 to 2 m2 at a few keV). The technology exploits the high-quality of super-polished 300 mm silicon wafers and the associated industrial mass production processes, which are readily available in the semiconductor industry. The plan-parallel wafers have a surface roughness better than 0.1 nm rms and are diced, structured, wedged, coated, bent and stacked to form modular Silicon Pore Optics, which can be grouped into a larger optic. The modules are assembled from silicon alone, with all the mechanical advantages, and form an intrinsically stiff pore structure.
The optics design was initially based on long (25 to 50 m) focal length X-ray telescopes, which could achieve several arc second angular resolution by curving the silicon mirror in only one direction (conical approximation).
Recently shorter focal length missions (10 to 20 m) have been discussed, for which we started to develop Silicon Pore Optics having a secondary curvature in the mirror, allowing the production of Wolter-I type optics, which are on axis aberration-free.
In this paper we will present the new manufacturing process, the results achieved and the lessons learned.
Future high energy astrophysics missions will require high performance novel X-ray optics to explore the Universe beyond the limits of the currently operating Chandra and Newton observatories. Innovative optics technologies are therefore being developed and matured by the European Space Agency (ESA) in collaboration with research institutions and industry, enabling leading-edge future science missions.
Silicon Pore Optics (SPO) [1 to 21] and Slumped Glass Optics (SGO) [22 to 29] are lightweight high performance X-ray optics technologies being developed in Europe, driven by applications in observatory class high energy astrophysics missions, aiming at angular resolutions of 5” and providing effective areas of one or more square meters at a few keV.
This paper reports on the development activities led by ESA, and the status of the SPO and SGO technologies, including progress on high performance multilayer reflective coatings [30 to 35]. In addition, the progress with the X-ray test facilities and associated beam-lines is discussed [36].
Silicon Pore Optics (SPO) is a lightweight high performance X-ray optics technology being developed in Europe, driven by applications in observatory class high energy astrophysics missions. An example of such application is the former ESA science mission candidate ATHENA (Advanced Telescope for High Energy Astrophysics), which uses the SPO technology for its two telescopes, in order to provide an effective area exceeding 1 m2 at 1 keV, and 0.5 m2 at 6 keV, featuring an angular resolution of 10” or better [1 to 24].
This paper reports on the development activities led by ESA, and the status of the SPO technology. The technology development programme has succeeded in maturing the SPO further and achieving important milestones, in each of the main activity streams: environmental compatibility, industrial production and optical performance. In order to accurately characterise the increasing performance of this innovative optical technology, the associated X-ray test facilities and beam-lines have been refined and upgraded.
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