This deliverable reports on the first survey of the in situ and ancillary data requirements of the CoCO2 project from tasks across work packages (WPs) 2 through 6. These requirements need to be documented to transition the project from a scientific exercise to an operational capacity, so that data dependencies and potential weak links in the future provision of timely flux estimates can be identified. The data needs were collected with an online survey, and responses were received from 16 participants across nine different tasks. Based on these responses, the identified data needs across 13 types of in situ measurements and 8 types of ancillary data products have been documented. Particular attention was paid to the timeliness requirements of the data, in addition to other specifications such as spatial coverage, temporal resolution, and where the project participants are currently accessing the various data streams. While it is clear that much of the data are needed in a timely manner, only one respondent reported a current need for near-real-time observations. However, because the data needs are still evolving over the first year of the project, this report reflects only a snapshot of data usage at this interim stage. This is a living book of requirements and will be updated annually over the three years of the project.