# INSPIRE-SAT 7, a Second CubeSat to Measure the Earth's Energy Budget and to Probe the Ionosphere
## 2 Scientific Objectives of the INSPIRE-SAT 7 Mission
### Earth's Energy Budget Components and Earth's Energy Imbalance
From mid-2005 to mid-2019, the EEI trend appears to be primarily due to an increase in absorbed solar radiation associated with decreased reflection by clouds and sea-ice and a decrease in outgoing longwave radiation (OLR) due to increases in the levels of greenhouse gases and water vapor. These changes combined exceed a positive trend in OLR due to increasing global mean temperatures. To date, the best estimate of the Earth's energy imbalance is obtained from the change in the heat accumulated in the ocean. However, the absorption of heat by the ocean acts as a buffer, slowing the rate of surface warming. The ocean heat content measurements performed by the Argo automated floats are excellent but the accuracy of the global mean estimation is hampered by the limited spatial sampling of the Argo network. In addition, the absorption of heat by the ocean acts as a buffer, slowing the rate of surface warming. Ocean heat content data do not contain much information on'short-term' dynamics. To solve the'short term' dynamics, one needs fine spatio-dynamics of the EEI. An important consideration is the temporal resolution of EEI estimates, as stated previously. A single satellite, typically on a Sun-synchronous orbit like the ERB satellite, can only provide measurements at two specific local solar times along the satellite trace and therefore resolve poorly diurnal variations. Diurrally-resolved ERB measurements are crucial for improving the representation of the fast physical processes in climate models, notably key cloud parameterizations. A constellation of small satellites, for instance in a trailing formation (multiple satellites orbiting on the same path separated by a specific time to view at different local times) with instruments that combine measurements with a narrow field of view and a wide field of view would represent an interesting strategy and a major step in our capabilities in monitoring EEI on a diurnal scale. The 'long-term' behavior of EEI is associated with the convolution of rapid processes and dynamic phenomena at longer temporal and spatial scales of the atmosphere/ocean system. Thus, in that case, the best strategy for monitoring EEI on long time scales is to follow the 'long term' temporal evolution of the thermal content of the oceans since the greatest part of the excessive heat (89% over the period 1970-2018) is absorbed by the ocean [3]. Nowadays,'short-term' measurements of ERB components at high spatio-temporal resolution have to be a priority. These measurements using a small satellite constellation (called Terra-F thereafter) are crucial for advancing our understanding of climate change because the radiative balance is partly driven by the radiative impacts of aerosols and clouds, which are highly variable spatially and temporally (with a strong diurnal scale) and are still relatively poorly quantified. These measurements would also allow constraining better poorly known radiative forcing associated with surface albedo and UV solar irradiance. A small satellite constellation can provide a global, 24/7 coverage that could improve the spatio-temporal sampling of ERB'short-term' measurements (day and year) owing to incoming solar radiation, which has the largest effect on the radiation balance, followed in importance by the cloud cover. The relevant scientific objective is to obtain ERB'short-term' measurements with fine spatial resolution (a few tens of km) and a temporal resolutions of three hours (comparable to the temporal scale of meteorological forecast) with an accuracy of a few \(\mathrm{Wm}^{-2}\). The UVSQ-SAT CubeSat [1] launched in 2021, represents our first pathfinder for a constellation to measure the ERB components and EEI. The objective is to establish that miniaturized broadband radiometers absolutely calibrated through an extensive calibration program can be built and operated in space for measuring the ERB components with an excellent accuracy. INSPIRE-SAT 7 is our second CubeSat dedicated to the measurements of the ERB components.