# HYPSO-1 CubeSat: First Images and In-Orbit Characterization
## 3 In-Orbit Payload Performance
### Spatial Resolution
#### 3.1.1 Ground Resolvable Distance (GRD)  
Here, first a qualitative and then a quantitative characterization of the pixel-level spatial resolution for HYPSO-1 in terms of GRD is presented. The aforementioned workdoes not discuss the potential adverse effects the atmosphere can have on resolving ground targets, and it is not further discussed here. In Figure 5, an image from an agricultural field near the Euphrates/Tigris estuary is used to assess HYPSO-1's sharpness. The lines in the field are due to roads and irrigation lines. The width of the lines running diagonally in the image is found using high-resolution satellite imagery to be about 50 m across. Selected bands across the spectral range are shown of the field closeup. The sharpness increases from 400 nm to about 530 nm and then decreases again from 565 nm to 800 nm. The sharpest bands are around 530 nm to 565 nm. Below 460 nm, and above 702 nm, the spatial images appear blurry. Worse spatial resolution at above 600 nm and below 500 nm is also consistent with the results from Figure 6, described in the following paragraphs. Note that the increased blurriness is predominantly in the horizontal direction of the images, which corresponds to the across track direction. The blurriness in the vertical or along track direction is in large part determined by the way the push broom scanning is performed as opposed to optics. The quantitative sharpness analysis used the spatial resolution assessment method described in [37; 38]. This is a processing pipeline for sharpness assessment for remote sensing data originally developed for sensors with a poorer spectral resolution. The method estimates multiple spatial resolution metrics, among them the FWHM of the LSF and the Relative Edge Response (RER). This estimation is carried out for several automatically detected suitable edges and repeated for every band. To estimate the LSF FWHM, an image of a thin (meaning smaller than the GSD) line with sufficiently distinct reflectance properties compared to the scene background is to be imaged. Alternatively, LSF can be estimated by differentiating the edge response, or the Edge Spread Function (ESF). The ESF is found by considering the sharp edge between two contrasting regions in the image [35]. Values for the LSF FWHM between 1.0 and 2.0 are associated with a balanced sharpness performance, while values higher than 2.0 are associated with blurry images. Ideally, one would have a LSF FWHM average close to 1.5 [37]. For comparison, the HICO instrument reported a maximum FWHM of the Point Spread Function (PSF) 1.6 [8]. Multiple images of various scenes were analyzed, with similar results. Results from the particular image in Figure 6 are shown as most edges were found in this image which is an indication of confidence in the results. Figure 6 shows the results of the FWHM of the LSF estimation, with the image on which the assessment was performed to the right. The plot to the left in Figure 6 shows the mean of the estimated LSF FWHM for each band in a data cube, in addition to a histogram of the number of suitable edges used for the sharpness  
Figure 5: A qualitative look at the image cube’s sharpness at different wavelengths. The bands used for the RGB composite representation are 602.5 nm, 565 nm and 498.4 nm, respectively. Reductions in GRD at higher and lower wavelengths shown in Figure 6 are visible (See subfigures (**A**,**F**,**G**)). The resolution is worse, mostly in the across-track direction, characteristic of a push-broom scan with little overlap. assessment for each band. Some bands at the extremities are removed as no suitable edges were found. The edges found by the sharpness assessment are almost exclusively in the across-track direction. Thus, this analysis characterizes only the across-track resolution. The mean LSF FWHM across all bands is 2.45 pixels. The best-performing bands have a LSF FWHM average below 2.4 pixels in the range 510 nm to 600 nm. The LSF FWHM for the sharpest band at 565 nm is 2.192 pixels.