The standard DMC Imager is a 6 channel, Surrey Linear Imager (SLIM6) and is built by Surrey Satellite Technology Ltd (SSTL), UK. The sensor is an evolution of previous multispectral cameras flown on various SSTL missions. The SLIM6 design provides for a nadir-viewing, three-band multispectral scanning camera capable of providing mid-resolution image information of the Earth's surface when operated from DMC spacecraft located in a near polar, sun-synchronous and circular orbit at a 686 km nominal altitude, with an orbit inclination of 98 degrees. The SLIM6 is designed to collect and detect radiation from the Earth in a swath 600 km wide as it passes overhead, utilising the spacecraft orbital motion to provide an along-track scan (push broom configuration). As a DMC image is acquired the CCD scan lines for each of the 6 channels are stored in a Solid State Data Recorder (SSDR) in a band-interlaced RAW format format. A separate SSDR is used to store data from each bank of three CCDs as it is acquired.

SLIM6 Design

The SLIM6 consists of 2 banks (Port and Starboard) of 3 channels (bands) and therefore 6 separate channels collect scene energy, as depicted below. Combination of the 2 banks provides the total nominal swath width in satellite view of 600km.

SLIM6 - Single Channel Focal Plane Assembly

Each SLIM6 imager channel has a solid-state detector at the focal plane.

The spectral filters for the bands are located in front of each channel lens. To protect the filter a fused silica radiation protection window is set in front of the filter (space facing).

Each channel lens is a Schneider Apo-Componon HM, this lens type has been flown on SSTL missions since 2000 (Tsinghua-1).

Description   Sensor Eastman Kodak KL10203 Linear CCD sensor. 10224 7.0 x 7.0µm pixel array   Lens Schneider Apo-Componom HM 150mm focal length, f/6.3   Lens data sheet FL value 150.9mm   iFoV 46.388µr = 0.00266 degrees = 9.568 arc sec   FoV (per channel) 2 x TAN-1 [(7x10-6 x 10200) / (2x150.9 x 10-3)] = 26.62 degrees   Swath (per channel) 31.822 x 10200 = 324.58km

SLIM6 - Spectral Filters

The nominal wavelength location of the SLIM6 spectral bands, nominal iFOV size and associated ground sample distance resolution, for a 686 km satellite altitude, are as shown in the table below. The SLIM6 spectral response is determined by the overall combination of all of the optical elements, the spectral filters, and the detector response. The spectral filters, located immediately in front of each channel lens, are the dominant items that establish the optical bandpass for each spectral band. Each SLIM6 Channel has a filter housing for the relevant filter as shown in Figure 1. Barr Associates Inc, USA manufactures the SLIM6 spectral filters with the same materials and processes as the Landsat ETM+ flight filters.

Band Channel Bank Bandwidth IFOV Sub Sat GSD Landsat Eqv   0 NIR 3 1 (starboard) 0.77 - 0.90µm 46.388µr 31.822m ETM+4 6 0 (port)   0.77 - 0.90µm   46.388µr   31.822m   ETM+4   1 RED 2 1 (starboard)   0.63 - 0.69µm   46.388µr   31.822m   ETM+3 5 0 (port)   0.63 - 0.69µm   46.388µr   31.822m   ETM+3   2 GRN 1 1 (starboard)   0.52 - 0.60µm   46.388µr   31.822m   ETM+2 4 0 (port)   0.52 - 0.60µm   46.388µr   31.822m   ETM+2

SLIM 6 - Sensor Model

The SLIM6 consists of 2 banks (Port and Starboard) of 3 channels (bands). Commonly both banks are used for image acquisition and the angle of the banks provides an overlap in the observed scene for corresponding bands/sensors in the opposite bank. This overlap is used to ensure accurate multiple image overlay or recombination. The nominal overlap based on in orbit calibration data is 567 pixels.

Parameter   Nominal Value Vertical Angle 25.2896 degrees Focal Length 21557 detector units Number of detectors 10224 Overlap between banks 567 detectors Clock Period 8.0E-7