The mission payload is the eponymous instrument based on a concept of acquisition pushbroom (therefore without scanning mechanisms) and that provides hyperspectral images of the Earth in the visible band and near infrared (VNIR) and short infrared (SWIR) to a spatial resolution of 30 m. The tool also includes a panchromatic channel (PAN), whose higher-resolution (5 m images) give a great added value allowing the development of techniques of fusion images.
PRISMA is characterized by high radiometric performance in terms of Signal-to-Noise Ratio (SNR) and a very high spectral resolution that allows the simultaneous acquisition of a large number of spectral bands in the 400-2500nm range.
To achieve this performance it is necessary to use spectrometers prisms which, together with a telescope only three mirrors, allow to obtain a very high transparency of the entire optical system.
The PRISM payload includes internal calibration unit that will verify the calibration of the hyperspectral sensor during the mission. This will enable the production of data / radiance images to high quality sensor. Moreover, the high number of spectral channels that characterizes the hyperspectral sensor in the region ranging from the VIS (400 nm) at the SWIR (up to 2500 nm) allows to carry out with greater precision the atmospheric corrections with the ability to accurately estimate the ' abundance of the main atmospheric constituents.

 

Orbit Altitude Reference

615 km

Swath / FOV

30 km / 2.77°

GSD

Hyperspectral: 30 m

PAN: 5 m

Spatial Pixels

Hyperspectral: 1000

PAN: 6000

Pixel Size

Hyperspectral: 30x30 μm

PAN: 6.5x6.5 μm

Spectral Range

VNIR: 400 – 1010 nm

SWIR: 920 – 2500 nm

PAN: 400 – 700 nm

Spectral Sampling Interval (SSI)

≤ 12 nm

Spectral Width

≤ 12 nm

Radiometric Quantization

12 bit

VNIR SNR

>200

SWIR SNR

>100

PAN SNR

> 240

Absolute Radiometric Accuracy

Better than 5%

Cooling System

Passive Radiator

Lifetime

5 years

 

The following diagram shows the functional blocks of the payload:

The following pictures show the optical layout of the two sides of the optical bench: on top are positioned optical elements of the telescope and the internal calibration unit and the bottom part are arranged the three channels (PAN, VNIR and SWIR) and the related detectors.


The following diagram shows the data processing steps on the raw data acquired by the VNIR and SWIR detectro and possible within the Main:

 

(1) Spectral selection
Through a software selection directly applicable on the detector is possible Optionally select the spectral line to be acquired. The baseline provides for the acquisition and the transmission of all the spectral bands of each detector

(2) Spectral binning
This optional feature implements a sliding window integrator of two successive spectral samples. The baseline does not include any spectral binning.

 (3) Spectral decimation
This optional feature implements a spectral decimation. The baseline provides no spectral decimation.

(4) Spatial grouping
This optional feature implements a spatial grouping of multiple samples. The baseline does not include any spatial grouping.
 

(5) Compression
An algorithm CCSDS-123 default is applied to dat idei VNIR and SWIR channels so as to reduce the data without affecting image quality.

(6) Packing, Encoding and Transmission
Scientific data processed in accord with previous blocks, housekeeping and ancillary data are then formatted according to the CCSDS standard.
A Reed Solomon coding (255.239) Interleaving 8, is applied to make the transmission resistant to any possible errors in the downlink to the ground.