IEEE Geoscience and Remote Sensing Magazine - June 2022 - 337

Today, the ESA considers QC and artificial intelligence
taking center stage for the implementation of Digital Twin
Earth (https://www.esa.int/Applications/Observing_the
_Earth/Digital_Twin_Earth_quantum_computing_and
_AI_take_centre_stage_at_ESA_s_Ph-week). Although
QC technology concepts are broadening and growing in
qubit capacities, their applications in RS and QML may
have unexpected results. The analysis of data complexity
and identification of optimal data embedding may
open novel perspectives. For instance, signatures of satellite
images could be encoded as quantum states and
transformed using quantum kernels for classification.
It might be feasible to encode a time-varying sequence
of EO images on a quantum state and analyze it using
a quantum computer to understand changes to the
Earth's surface. But to achieve that, more efforts in both
the theoretical development of quantum algorithms and
quantum hardware design and production will have to
be made to push the boundaries of what is possible to
achieve with QC. An important aspect is the close collaboration
with quantum computer developers and providing
appropriate requirements [e.g., the European Quantum
Industry Consortium (https://qt.eu/about-quantum
-flagship/the-quantum-flagship-community/quic/)].
BLOCKCHAIN
Open data have become a significant vector in all of the
services consumed today, as enormous quantities of data
are quickly accessible. Most of the time, distributing and retrieving
data are drained through mediators, which impose
control and evaluation policies for reliability and integrity
of the data. As connections between data owners and data
consumers are generally maintained through a central authority
for practical goals, thus limiting the actions of users,
intermediary technologies are necessary to ensure trust
among participants, data availability, data validity, and
data integrity, all in a transparent way.
The advent of technological progress and evolution in
open source and distributed ledger technologies (DLTs)
has demonstrated that it is possible to develop systems that
prioritize individual jurisdiction over centralized control.
Distributed ledgers are collections of replicated, shared,
and synchronized digital records that are stored across
multiple geographically disseminated sites. A blockchain
is an example of a DLT that is fundamentally an appendonly,
permanently verifiable data structure maintained by
a set of nodes that do not fully trust each other. These nodes
comply with a set of global states for an ordered collection
of blocks, each containing multiple verification records
(i.e., transactions). Each block is linked in a chain of blocks
where the subsequent block, additionally, has a verification
record of the previous block (i.e., a unique hash fingerprint).
In this way, it is impossible to add new information
to older blocks in the chain without changing subsequent
blocks. Each node keeps replicas of the data and grants an
execution order, thus producing an immutable log of orJUNE
2022 IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE
dered transactions within a distributed transaction management
context.
Blockchains have manifested great promise in several
fields like cryptocurrency (Bitcoin [144], Ethereum [145],
and so forth), governance, land registration, justice, identity
management, asset tracking, and the IoT, materializing
in large-scale adoption as the result of solving limitations in
previous systems. Blockchain technology has also started
to evolve within the new space sector (i.e., Space 4.0) over a
range of potential applications, from satellite communications
to procurement. In a white paper, the ESA accentuated
the relevance of assimilating blockchain into RS applications
[146], supporting action automations through
smart contracts and transfer of value without a pivotal
authority. The data gathered via close-range sensors, e.g.,
IoT sensor networks or personal drones, can massively enrich
EO applications in consistency and accuracy. The data
owners can keep ownership, providing reliability through
a blockchain solution.
Due to the verifiable and immutable nature of blockchain's
technology, it can be used as a distributed database
of digital fingerprints (e.g., mapping, cadastre, land registration
[147], sharing continuously updated ML models
[148], and so on.) As corruption can be a big challenge
within administrative systems, the registration of land and
real estate ownership using blockchain enhances transparency
and accountability, bringing actors in control
of their own data. The enormous repositories of data are
transformed in intrinsically public open data by adopting
blockchain and related technologies like the InterPlanetary
File System [149], where no one controls data, anyone
can access data, and anyone can audit the entire history
of inputs. Novel blockchain protocols can also be used to
precisely map physical world events in a temporal progression.
For instance, cryptospatial coordinate (CSC) is an
open and interoperable standard for location in Ethereum
smart contracts. FOAM [150] is a CSC blockchain protocol
that preserves geospatial data by validating the proof of location
associated with the entry's specific time.
Blockchain technology brings important contributions
in process management within complex systems, offering
capabilities of managing massive patterns of transactions
in any combination of two entities: human and device.
SpaceChain builds an open source satellite network [151] in
which satellites incorporate blockchain as an operating system
and interface for decentralized applications to permit
individuals to work on collaborative projects, with smart
contracts on a space-based computing platform.
Blockchain can improve space communications and
navigation, where the risk of transmission disruption can
be eliminated by developing a decentralized, secure, and
cognitive networking and computing infrastructure for
deep space exploration [152]. A decentralized schema for
verifying satellite locations in time through a type of proofof-location
protocol is proposed in [153]. The intent in using
a permissioned blockchain is to facilitate scalability and
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https://www.esa.int/Applications/Observing_the https://www.qt.eu/about-quantum
IEEE Geoscience and Remote Sensing Magazine - June 2022

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