## 4 Ground Segment
### Acquisition Plan and Operations  
EnMAP is able to acquire 5000 km along-track per day with 30 km across-track based on the acquisition requests of users that are specified via an online interface [53]. A user request consists of:  
* Center of the geographical area of interest between 80\({}^{\circ}\) north and 80\({}^{\circ}\) south. * Length of the geographical area of interest as a multiple of 30 km and up to 1000 km. * Definition of the allowed maximum across-track satellite tilt angle (between 5\({}^{\circ}\) and 30\({}^{\circ}\)). * Time period when the acquisition shall be executed. Acquisitions are planned for the descending orbit. Only observations with SZA \(<\) 60\({}^{\circ}\) are considered in order to guarantee acceptable illumination conditions. Table 2 illustrates the resulting revisit capabilities in descending orbits for six different latitudes and two values of the maximum across track tilt angle. All areas of interest in Table 2 can be observed with a tilt angle lower than 3.1\({}^{\circ}\). Although EnMAP is based on an open data policy and every type of user is in principle entitled to download data and request acquisitions, there will be different user categories to set acquisition priorities. In short, Category 1 users (Cat. 1) will be scientific users who have submitted a research proposal \begin{table}
\begin{tabular}{c c c c c c} \hline
**Latitude** & **Area of Interest** & **Max RT** & **Mean RT** & **Max RT** & **Mean RT** \\  & & **with TA \(<\) 30\({}^{\circ}\)** & **with TA \(<\) 30\({}^{\circ}\)** & **with TA \(<\) 5\({}^{\circ}\)** & **with TA \(<\) 5\({}^{\circ}\)** \\ \hline
0\({}^{\circ}\) & Libreville, Gabon & 4 days & 3.4 days & 27 days & 19.9 days \\
15\({}^{\circ}\) & Niger, Niger & 4 days & 3.2 days & 27 days & 18.2 days \\
30\({}^{\circ}\) & Tripoli, Libya & 4 days & 2.8 days & 27 days & 16.3 days \\
45\({}^{\circ}\) & Munich, Germany & 4 days & 2.3 days & 23 days & 11.5 days \\
60\({}^{\circ}\) & Oslo, Norway & 3 days & 1.5 days & 19 days & 8.1 days \\
75\({}^{\circ}\) & Longyearbyen, Norway & 1 days & 0.7 days & 7 days & 3.7 days \\ \hline \end{tabular}
\end{table} 
Table 2: Maximum and mean revisit time (RT) in descending orbits for six different latitudes, represented by areas of interest, and two maximum across track tilt angles (TAs). describing how they plan to use the data. Scientific proposals will be evaluated and rated by the EnSAG and potential external reviewers. In turn, Category 2 users (Cat. 2) will be non-registered international public or private entities. The priorities for requests to be considered are, in decreasing order: internal (e.g., calibration), emergency Cat. 2 (e.g., international charter on space and major disasters), Cat. 1 (with high rated scientific proposal), Cat. 1 (with low rated scientific proposal), non-emergency Cat. 2, internal (low, e.g., to fill up or extend requests). Requests of the first two priorities are scheduled regardless of their success concerning cloud probabilities or quota. Thus, especially requests of the last four priorities shall take the revisit times into account for setting the time period appropriately to increase the probability that the scheduling fulfills the request. Of course, this depends on the specific area of interest and further requirements on the observation. Whether a specific user request is scheduled for execution is based on:  
* Satellite resources (e.g., available data storage, scheduled data downlinks and orbit maneuvers for orbit maintenance or collision avoidance). * Quota, e.g., 80% for all Cat. 1 users (registered) in the first year to 60% in the fifth year, where internal users are not considered. * Cloud probabilities (e.g., historical and predicted cloud coverages). The users shall place a request at least 25 h before the intended execution to ensure its uplink, because an S-band contact (4 Kbit/s uplink, 32 Kbit/s downlink) via the Weilheim, Germany, multi-mission ground station is scheduled at least every 12 h and planning of the conflict-free sequence of events takes one hour.