IEEE Geoscience and Remote Sensing Magazine - September 2021 - 27

(WMO's) " Vision for WMO Integrated Global Observing
System (WIGOS) in 2040 " report [6] and the recent
" NOAA Satellite Observing System Architecture (NSOSA) "
study [7]-[9].
This article focuses on the components of the EOSC
that are useful for weather forecasting and a multitude of
environmental applications, particularly global NWP. We
frequently choose NWP as an example because it is well
established and foundational in the sense that many other
applications rely on NWP analyses and forecasts for inputs,
constraints, or boundary conditions. When the applications
are considered together, we highlight that the requirements
placed on the EOSC become significantly more
complex and point to the importance of all the observing
systems, even those with seemingly redundant capabilities.
The growth of the EOSC has been multifaceted, including
increases in the number of satellites deployed; the number
of countries and institutions involved in developing and
deploying them; the types of orbits, sensors, and techniques
employed to monitor Earth's environment; and, most importantly,
the diversity and quality of the observations. This
growth in space-based capability has been accompanied by
an equally explosive expansion in the scientific understanding
of Earth's system and our ability to exploit space-based
data as well as in the number of applications, services, and
users that rely on these satellite measurements.
This growth in both capabilities and applications has
been driven by
1) advances in remote sensing technology, leading to innovative
ways of observing the environment
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2) ever-expanding user requirements for additional data
with more accuracy and more coverage in time and space
OBSERVING SYSTEMS OF THE FUTURE
The EOSC is a collection of satellites and sensors that make
observations for meteorology and other environmental
sciences. The EOSC monitors and aids in the prediction of
many important phenomena, such as hurricanes, severe
storms, floods, and droughts. The EOSC began in 1960,
when TIROS-1, the first meteorological satellite, demonstrated
the extraordinary capabilities offered by space-based remote
sensing systems (see " Acronyms Used in This Article " ).
From the first TIROS-1 photographs of clouds from space, the
global satellite system has evolved to support many societal
application areas and has been a key factor in the dramatic
improvement in weather forecasts and warnings.
Since its inception, the EOSC has experienced a rapid
growth in the diversity and number of its sensors and satellites
[1], which, together with advances in technology,
have resulted in a very substantial increase in the number
and types of observations available (see, e.g., [2] and
Figure 1). A number of earlier studies highlighted the importance
of the global observing system [3]-[5]. Further,
several agencies have carried out extensive strategic exercises
to develop the foundation for future satellite systems.
These include the World Meteorological Organization's
SEPTEMBER 2021 IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE
3) research pioneering new ways to use observations in
models and other applications and to advance the science
4) the increasing number of nations and nongovernmental
entities having access to space with the capacity and desire
to deploy Earth-observing satellites.
In WMO nomenclature, all of the satellite sensors that
comprise the EOSC are known as space based; the other sensors
(essentially, everything suborbital) are termed surface
based. Surface-based sensors are also crucial for monitoring
the environment. The space- and surface-based components
feature different and complementary observing
characteristics: For instance, high spatial and temporal
resolution is obtained from surface-based weather radars
but with limited spatial coverage, while space-based radars
offer global coverage but have coarser horizontal resolution.
It should be noted that the data from the diverse
observing systems are mutually beneficial for calibration
and validation purposes, e.g., in [10] and [11], as well as for
identifying rogue observations (i.e., outliers) and instrument-quality
issues. In this article, we focus on the spacebased
components while recognizing the importance and
complementarity of surface-based components.
Space-based sensors observe different environmental
domains, including the atmosphere, oceans, and land
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IEEE Geoscience and Remote Sensing Magazine - September 2021

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