# A Blockchain Solution for Remote Sensing Data Management Model
## 3 The Architecture of the System
### Block Data Structure Serving Large-Scale Remote Sensing Applications  
For different remote sensing data providers with different requirements for data security, suitable blockchain data structures are designed for multi-chain structures, respectively. This study constructs a new data structure in the blockchain as a prerequisite basis for remote sensing data storage and sharing. In view of current problems, such as large differences in the quality of Earth observation information products, and no unified evaluation index of information products for domain applications, we study the block storage model based on the open and recordable features of access to data, and operation process information under the interoperable environment, and form an efficient and distributed blockchain storage scheme for remote sensing data, to ensure security and efficient access to data. Blockchain technology can make the data in the blockchain more valuable. By multiple nodes participating in data recording together and verifying the accuracy and validity of their information with each other, they can achieve the all-around confirmation and verification of information, thus eliminating uncertainty and reaching consensus. The blockchain stores the data storage records of different users and the data storage addresses on IPFS, and the stored records are guaranteed not to be tampered with, as they generate unique hash values through hash functions. This study analyzes the remote sensing data storage aspect and proposes a generic block data structure, to store the related data with state attributes and remote sensing attributes, and to query them based on the uniqueness of the path. The raw remote sensing data are stored on IPFS, and when the file is uploaded to the IPFS node for storage, the node will organize the file in the Merkle Directed Acyclic Graph (Merkle DAG) format for block storage and, after the storage is completed, the file will be represented by the root hash number of the Merkle DAG, and the user can build the network from IPFS via Distributed Hash Table (DHT) Get the file. Through hashing the recorded data blocks and storing the hash values in the blockchain, there is no need for nodes to have massive storage space. Once the content is modified, the corresponding hash value will also change, and cannot be matched with the hash value in the blockchain, ensuring the unmodifiability of the content. The hash value ensures that the data are trustworthy and has not been tampered with, so that accurate backtracking can be achieved, and the property rights of the data are guaranteed. As remote sensing data have a strong professionalism compared with general data, in addition to remote sensing image information, they also needs to save their descriptive information of the remote sensing image data themselves, including spatial, spectral, and temporal dimensional information, etc. They need to save metadata information, especially for easy finding; through metadata, we can easily query the remote sensing data we want to access, without exposing confidential data at the same time. Therefore, we divide the remote sensing raw data into two files, remote sensing image data, and metadata, and perform a hash calculation on them separately. In the multi-chain structure designed in Section 3.2, the public chain is used as the main chain to store the remote sensing open data and the summary of the federated chain blocks. Considering the different identities of the data providers, the remote sensing data center should provide a data-sharing platform between them, to facilitate collaborative operations, while the open data providers should ensure data trustworthiness, and data privacy protection, to solve the problems of mutual trust, and data authenticity and confidentiality. As shown in Figure 3, this paper divides the public chain blocks into two types; one is to record the various transaction data in the alliance chain, which are recorded as Class A blocks.