# HYPSO-1 CubeSat: First Images and In-Orbit Characterization
## 3 In-Orbit Payload Performance
### Spectral Resolution
The resulting filtered and normalized responses of the reference spectrum and full resolution data (1 frame) are shown in Figure 10, showing comparable features from the Fraunhofer lines in the datasets. Figure 8: Convolved reference irradiance. Solar irradiance spectrum at 1 nm resolution convolved with a set of instrument responses to obtain simulated solar irradiance spectrum at different spectral resolutions. Figure 10: Comparison with reference spectra. HYPSO-1 data (black) and solar spectrum at different simulated spectral resolutions (shades of blue), after filtering and normalization. Figure 9: Raw spectrum of the Moon captured by HYPSO-1, with (orange) and without (blue) binning (spectrally binning nine pixels). Reducing noise by averaging 10 frames (without binning) is shown in green. Normalized intensity is recorded digital counts divided by the mean value in the spectrum. The solar spectrum was simulated at resolutions between 3.3 nm (theoretical limit of HYPSO-1) and 10 nm, with 0.1 nm steps. The spectra were compared by using Root Mean Square Error (RMSE) between the HYPSO-1 spectrum and reference spectra, and best fit determined as the one with the lowest RMSE value. The results are presented in Table 5. The solar spectrum with spectral resolution of 5.4 nm was found to be the best fit within the range of 430 nm to 780 nm for the full resolution data (1 frame) and 5.6 nm when 10 frames were averaged first. With binning, the same analysis gives the average spectral resolution over the same range to be 8.2 nm. It was shown in [24] that the spectral resolution varies with wavelength, where it was measured to be between 3.5 and 4.5 nm for HYPSO-1 prior to launch (for full spectral resolution data). The best resolution was found above 700 nm, while wavelengths between 430 nm and 700 nm had resolution calculated to be roughly between 4 nm and 4.5 nm. The analysis here was therefore repeated for only parts of the spectra, in 50 nm bands starting at 430 nm and ending at 780 nm, i.e., 430-480, 480-530, etc. The best fit spectral resolutions in those bands and RMSE of the fit are presented in Table 5. The highest (lowest number) estimated spectral resolution of the full resolution data (both 1 frame and 10 frames average) is 3.4 nm, found in bands 630-680 and 730-780, which is close to the theoretical limit of 3.3 nm 3.3 nm. The lowest (highest number) for the full resolution data are 6.6 nm (1 frame) and 7.2 nm (10 frames average), which is found between 530 nm and 580 nm. This coincides with the trends seen in [24]. For the binned data, the highest spectral resolution is found at 730 to 780 nm, and is 4.0 nm, while the lowest is found at 430 nm to 480 nm to be 9.60 nm. Similar to the findings in [24], the resolution is best at longer wavelengths (above 600 nm), and worse for the binned data. The signal recorded for short and long wavelengths is relatively low so SNR is lower, as seen in Figure 9. In the range 730-780 nm, the estimated spectral resolution is worse for the full resolution single frame than the binned data. This is likely to be because the binned data are smoothed so the noise is reduced. The RMSE value gives insight into how large deviation was found between the solar spectrum of estimated resolution and the measured HYPSO-1 spectra, with low RMSE values meaning similar spectra. However, mismatch between the spectra can also come from different intensities not being fully filtered out, leaving residue from the reflected light of the scene (the Moon), or from spectral shifts between the spectra. It is therefore important to make sure the spectra are properly filtered and aligned before the analysis. One reason for the RMSE varying between the different spectral ranges can be due to different features at different locations in the spectrum, making some regions easier to match up than others. It can be noted that the 630 to 680 nm range has high RMSE compared to the other ranges, most likely due to few features being present in this region.