**5. Reference Instrument Selection**

The main requests of any satellite monitoring mission can be summarized as follows: (1) that observations are acquired with the required revisit time; (2) preferably in all weather conditions (clouds, rain, haze, and fog) and in all illumination conditions; (3) with a large swath to reduce the revisit time; (4) with the required radiometric and spatial resolutions; (5) with low manufacturing and launch costs, and with minimum deployment time in case of failure; and (6) keeping these parameters in mind, the reference instruments can be selected. In this way, the identification of instruments is based on the state-of-the-art at the payload level and the need to fulfill the gaps of the current Copernicus infrastructure.

Reference instruments and small platforms have been selected in the previous chapter. In this way, it has as strategy been implemented a significant reduction of the development time and cost, thanks to the adoption of commercial technologies, but it requires that these have a good performance of the measurement capabilities. In this regard, the capability of the instrument technologies is evaluated according to the trends in the design for small satellites. For each instrument, the mass and power consumption constraints, and data quality (spatial resolution, swath, and accuracy) are taken as a reference. This chapter evaluates if the instruments selected to meet the requirements (defined in [6]) in terms of spatial resolution and accuracy. Table 8 summarizes the performance requirements over each instrument:



**Table 8.** Reference instruments selected to cover the measurements with gaps.


**Table 8.** *Cont*.

*<sup>a</sup>* antenna size of 2.2 m. *<sup>b</sup>* antenna size 3.4 m. The background color in the requirements denotes: Green: Requirement met or is better; Yellow: Minimum requirement met; Red: Have worst performance that the minimum requirement. The background color in the instrument indicates the platform suitable according to the power and mass requirements: Very light gray: Nano-platform; Light gray: Micro-platform; Gray: Mini-Platform.
