Objectives of the Product

The understanding of extreme precipitation events is of critical interest for scientists as
the frequency of those events is likely to increase and as they have a direct impact on
many human activities (e.g., agriculture, logistics, accessibility to water, landslides or
flood prevention, natural disasters) with devastating socio-economic consequences.
Those events are controlled by moisture, but there is an absence of efficient
measurements of such moisture profiles when precipitation occurs. By leveraging the
capabilities of the CubeSat platform and growing experience on processing and
analyzing GNSS-RO Data, Spire proposes to alleviate the heterogeneity and limitation
of existing sensing solutions (infrared, radar, …) with an approach that could deliver
valuable precipitation data, globally, with the potential to scale to a large constellation
at a cost point that is substantially lower than today’s EO missions
This would potentially lead to a better understanding of events such as tropical
cyclones, as well as better validation tools for cloud and precipitation models,
improving weather forecasts.

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Customers and their Needs

There are 3 customer segments identified:

• National and multinational weather agencies / research and civil protection
  institutions: Needing accurate precipitation information, comparable and
  compatible with other existing terrestrial and space-based remote sensing
  systems, available during rapidly evolving precipitation events. There will be
  varying requirements and needs among them: historical data versus current
  and forecast; global versus regional; data latency; operational availability,
  etc.
• Application Service Providers: Designing tools to support operations of
  weather-exposed industries. Some of which are already existing customers
  of Spire. This customer segment is more interested in an accurate, reliable
  and affordable source of data, notably during rapidly evolving precipitation
  events
• End Customers: Having ‘in-housed’ the development of their own
  applications and related meteorological products and services, looking for
  quality weather information to support business critical applications (Agri
  business, Insurance, Airline operators, …) facing difficulties accessing data
  during rapidly evolving events
  Different institutions have already been approached and expressed interest in
  Spire’s development.

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Targeted customer/users countries

Interests have been raised in Europe as well as in American and UK based
institutions.

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Product description

The main product consists of vertically resolved profiles of GNSS-PRO which are
sensitive to the presence of precipitation and ice crystals as well as to temperature
and moisture. The data are obtained from an in-orbit demonstrator payload aboard a
CubeSat. These data produced by the GNSS-PRO sensor will be generated and
formatted as per Earth observation standards.
The main components of the product will be profiles of calibrated polarimetric phase
delay differences and derived features consistent with the vertical structures of
precipitation, as well as the conventional output of GNSS radio occultations;
combined together, they enable further capacities of detection such as the cloud top
height or to potentially distinguish convective from stratiform precipitation. This would
lead to a new data product to be fully embedded into Spire’s full range of weather
data products.

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Added Value

Spire sees GNSS-PRO as an incipient and innovative approach to the observation and
measurement of rainfall under all weather and day/night conditions, and in accordance
with an overarching vision to utilize GNSS signals of opportunity to generate valuable
weather products with an already proven ability to deliver in this domain.
The first and only space mission to carry a GNSS-PRO payload is the Radio
Occultation and Heavy Precipitation (ROHP) experiment aboard PAZ, a Spanish Earth
observation and reconnaissance satellite launched on 22 February 2018. Spire will
innovate beyond ROHP in the following key aspects:

• The instrument: With a new antenna and a new multiband receiver technology
• The integration of the instrument within a small sat platform
• The evaluation of the potential of this new data source for assimilation models

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Current Status

Several activities are under development in preparation for the proper launch of the
satellite:
● A mock-up design of the polarimetric antenna on a satellite was made and the
polarimetric radiation patterns were measured in an anechoic chamber to
account for multipath and cross-polarization
● An error model of the differential phase has been reviewed and updated to
include polarimetric imbalance, cross-polarization and attitude effects
● A revision of the state-of-the art PRO differential phase retrieval adapted to be
compatible with the implemented processing of GNSS-RO at Spire
● A general design of the ground processing architecture and files format is
proposed and discussed