In the past, PROBA-1 had carried onboard several Earth observation and space environment scientific instruments. The project's aim was to have demonstrated technology, as several platform elements and systems had been included as technology experiments.

Extensive use was made of automated functions onboard the spacecraft. Full onboard flight dynamics computation, in conjunction with past automated ground segment functions such as pass automation and high-level user interfaces, satisfied the spacecraft autonomy requirements.

Automated functions onboard had handled nominal spacecraft operations, planned and scheduled activities, and managed payload resources. The onboard flight dynamics included orbital navigation as well as computation and control of instruments, camera pointing, and scanning in order to have met user-defined targets (latitude, longitude, and altitude).

From its inception until its discontinuation in December 2022, CHRIS served as the prime instrument of the PROBA-1 mission, covering applications that included atmospheric, land, agriculture, and both oceanic and coastal observations. The technological objective was to explore the capabilities that imaging spectrometers would have on agile small satellite platforms.

The methodology used in the CHRIS-PROBA project was to sample top-of-atmosphere radiation in appropriate parts of the spectrum, and from different directions nearly simultaneously. Aerosol reflectance depends on the extinction coefficient. This in turn depends on the aerosol particle size distribution and on the wavelength of the light. 

The aerosol properties are retrieved by inversion of radiative transfer models. The enhanced spatial, directional and spectral sampling of the CHRIS-PROBA system promised further improvements.

CHRIS provided information on land cover type and areal extent and on the directional properties of surface reflectance, and hence infered properties about surface structure, especially of vegetation canopies.

CHRIS measured carbon fluxes in relation to global climate change, forestry productivity and forest condition.

CHRIS data are highly relevant to forestry studies. Of particular interest was the dual capability of CHRIS to acquire both hyperspectral and multi-angle data. The hyperspectral data supports species identification and mapping, as well as providing information about the impact of pollution and other environmental factors on forest production.

CHRIS provided data for studies into the relative contribution of leaf area index (LAI) and chlorophyll to the wavelength response provided by individual forest canopies. This had particular relevance to monitoring stress in forests.

CHRIS provided high spatial resolution and multi-temporal 'ocean colour' imagery.

All the priority water sites had in-situ sampling (optical and bio-geochemical) during the CHRIS acquisition periods. There are also:

• Sun photometer measurements
• Other forms of remote sensing (additional airborne/satellite systems).

The priority test sites were well characterised and represented a range of Case 2 waters*. 

(*The classification of ocean waters in "Case 1" and "Case 2" began with Morel and Prieur (1977). They wrote that two extreme cases can be identified and separated. Case 1 is that of a concentration of phytoplankton high compared to other particle. In contrast, the inorganic particles are dominant in Case 2. In both cases dissolved yellow substance is present in variable amounts. An ideal case 1 would be a pure culture of phytoplankton and an ideal case 2 a suspension of non-living material with a zero concentration of pigments. Morel and Prieur emphasized that these ideal cases are not encountered in nature, and they suggested the use of high or low values of the ratio of pigment concentration to scattering coefficient as a basis for discriminating between Case 1 and Case 2 waters. Although no specific values of this ratio were proposed to serve as criteria for classification, their example data suggested that the ratio of chlorophyll a concentration (in mg m-3) to the scattering coefficient at 550 nm (in m-1) in Case 1 waters is greater than 1 and in Case 2 waters is less than 1. Importantly, however, Morel and Prieur also showed data classified as "intermediate waters" with the ratio between about 1 and 2.2).