# HYPSO-1 CubeSat: First Images and In-Orbit Characterization
## 4 Discussion and Conclusions  
The HYPSO-1 CubeSat has started its journey of collecting ocean color data. Observational data are planned to be made available to the scientific community as soon as the calibration and validation phase is completed, and calibrated data products can be delivered. For nominal operations, 5-6 observations per day are possible due to mainly downlink limitations of around 450 MB per day. During campaigns, it is possible to acquire a higher number of observations, downlinking the backlog of data after each campaign as long as real-time data are not required. Throughout the paper, we discuss the five main mission Goals, repeated here for convenience:  
**Goal 1:** Data latency should be less than 1 h [25];
**Goal 2:** Revisit times to dedicated areas of interest should be 3-72 h [25; 26];
**Goal 3:** Images should have spatial resolution better than 30-100 m per pixel [3; 11];
**Goal 4:** The raw hyperspectral data should have a spectral resolution of about 5 nm or better, for VIS-NIR wavelengths [3; 11];
**Goal 5:** The SNR at ToA should be greater than 400 in visual wavelengths for open ocean water [33], and atmospherically corrected SNR of water-leaving signals should be between 40-100 [34]. For **Goal 1**, the data latency for raw data are shown to be closer to 4 h, with a single ground station. This can be significantly reduced with a ground station network, see [15] and Table 3 during the quick-response planning. The latency could also be reduced by using on-board processing to reduce the size of a dataset. The response time in the quick-response planning example is shown to be less than 1.5 h.  
The revisit time in **Goal 2** is mostly determined by the orbital properties of the satellite and the pointing constraints. Thus, the orbital period of 90 min and the location of the area of interest determine what is achievable for a given target. Targets above 60 degrees latitude (N or S) can have two consecutive passes with a 90-minute temporal separation, while targets above 70 degrees have at least three consecutive passes. Targets below 60 degrees, however, are limited to one pass per day. As small CubeSats are relatively cost-effective and scaleable, it is possible to improve revisit times by launching several. **Goal 3** is expected to be achieved in raw data with nadir pointing. The best spatial resolution in terms of GRD is estimated to be around 140 m under such conditions. Off-nadir captures increase the GRD proportionally. A higher off-nadir angle also increases the covered area. The Goal might still be achieved by significantly reducing GSD in a slewing maneuver and using super-resolution processing methods. The in-orbit data estimate the spectral resolution to be 5.6 nm on average and 5.4 nm in the area around 600 nm, slightly exceeding the value of 5 nm in **Goal 4**. There is, however,room for improvement in the analysis, and further work should be carried out to estimate the spectral resolution at each spectral band. For **Goal 5**, the ToA SNR is estimated to be at least 200 for the spectral region between 450 nm and 600 nm and above 300 for important spectral regions for looking at cyanobacteria. The regions used to estimate the SNR are at the center of the FPA, and it should be stressed that this is the region of the HYPSO-1 image sensor where the observed signal is expected to be the strongest, i.e., has the best noise characteristics. With the methods for noise estimation used in Section 3.5, the HYPSO-1 payload can deliver at the same level, or better, for certain parts of the electromagnetic spectrum, as illustrated in Figure 16, when compared to other relevant sensors. However, from this, the Goal of SNR characteristics of the payload is not met for the ToA signal but still performs at a high level. The Goal also aims at having an SNR of at least 40 for the water leaving reflectance--that is, the signal after correcting for effects from the atmosphere's constituents.