We present a novel 3-channel freeform imaging space spectrometer, covering visible, near-infrared and thermal wavelength bands, and featuring an extremely wide field-of-view of 120°, while fitting within a single CubeSat unit, exceeding the state-of-the-art designs.

A variation of the solar energy received by the earth – quantified by the Total Solar Irradiance (TSI) – is a radiative forcing for climate changes on earth. Since the 1976 Science paper by J. Eddy, solar-climate research has been dominated by the paradigm that solar activity and TSI have been slowly increasing since the Maunder Minimum - extending from about 1645 to 1715 – and the present, which was believed to be a Modern Solar Maximum. If this paradigm were valid, over the last 50 years, when most of the global warming has occurred, this warming would be partly due to anthropogenic greenhouse gas warming, and partly due to natural solar warming. However, evidence has been accumulating against the ‘Modern Solar Maximum paradigm’. Based on this evidence, recently a new reconstruction of the centennial TSI variation from 1700 to 2020 was published. This new centennial TSI reconstruction is nothing less than a paradigm shift for Sun-Climate research. Following the new TSI reconstruction, the TSI did not gradually increase over the last 320 years, but rather varied with a long term periodicity of 105 years, and currently we are near the minimum of this 105 year variation. Therefore over the last 50 years, the sun did not contribute to global warming, but rather tried to cool the earth, partly counteracting greenhouse gas warming. Since we are near the minimum of the 105 year variation, we can expect a trend reversal and for the next 50 years we can expect that the sun will contribute to global warming, making it more difficult for mankind to reach the goals of the Paris Climate Agreement, in order to avoid catastrophic climate change.

The Earth Energy Imbalance (EEI) is defined as the small difference between the incoming energy the Earth receives from the Sun and the outgoing energy lost by Earth to space. The EEI is accumulated in the Earth climate system and results in global temperature rise. Monitoring the EEI is of prime importance for a predictive understanding of climate change, and for estimating how well humankind is doing in implementing the Paris Climate Agreement.The current best estimates of the absolute value of the EEI, and of its long term variation are obtained from in situ observations. These observations can only be made over long time periods, typically a decade or longer. In contrast, with direct observations from space, the EEI can in principle be measured at the annual mean time scale. However, this strategy currently faces two fundamental challenges.The first challenge is that the EEI is the difference between two opposing terms of nearly equal amplitude. Currently, the Incoming Solar Radiation (ISR) and the Total Outgoing Radiation (TOR) are measured with separate instruments, which means that their calibration errors are added and overwhelm the signal to be measured. To make significant progress in this challenge, a differential measurement using identical intercalibrated radiometers to measure both the ISR and the TOR is needed.The second challenge is that the TOR has a systematic diurnal cycle. Currently, the TOR is sampled from the “morning” and “afternoon” Sun-synchronous orbits, complemented by narrowband geostationary imagers. Recently, the sampling from the morning orbit was abandoned. The sampling of the diurnal cycle can be improved, for example, by using two orthogonal 90° inclined orbits which give both global coverage, and a statistical sampling of the full diurnal cycle at seasonal time scale.For understanding the radiative forcing and climate feedback, mechanisms underlying changes in the EEI, and for climate model validation, it is necessary to separate the TOR spectrally into the Reflected Solar radiation (RSR) and Outgoing Longwave Radiation (OLR) and to map them at relatively high spatial resolution.The state-of-the-art observation of the OLR is provided by the CERES scanning 3-channel broadband radiometer aboard the Aqua, Suomi NPP and NOAA 20 satellites. We propose an innovative continuity of those measurements by replacing the radiometer by multispectral wide field of view (FOV) cameras. The wide FOV allows a full angular coverage, providing the potential for a significant reduction of the dominant angular conversion error. To realise this potential we propose to develop an innovative Deep Learning based angular conversion method. The multispectral bands of the camera should allow reconstructing the broadband OLR within the state of the art accuracy. The spatial resolution of the cameras should be sufficient to discriminate cloudy from clear-sky scenes.

Monitoring the Earth Energy Imbalance (EEI) is of prime importance for a predictive understanding of climate change. Furthermore, monitoring of the EEI gives an early indication on how well mankind is doing in implementing the Paris Climate Agreement. EEI is defined as the small difference between the incoming energy the Earth receives from the Sun and the outgoing energy lost by Earth to space. The EEI is cumulated in the Earth climate system, particularly in the oceans, due to their substantial heat capacity, and results in global temperature rise. Currently the best estimates of the absolute value of the EEI, and of its long term variation are obtained from in situ observations, with a dominant contribution of the time derivative of the Ocean Heat Content (OHC). These in situ EEI observations can only be made over long time periods, typically a decade or longer. In contrast, with direct observations of the EEI from space, the EEI can be measured at the annual mean time scale. However, the EEI is currently poorly measured from space, due to two fundamental challenges. The first fundamental challenge is that the EEI is the difference between two opposing terms of nearly equal amplitude. Currently, the incoming solar radiation and outgoing terrestrial radiation are measured with separate instruments, which means that their calibration errors are added and overwhelm the signal to be measured. To make significant progress in this challenge, a differential measurement using identical intercalibrated instruments to measure both the incoming solar radiation and the outgoing terrestrial radiation is needed. The second fundamental challenge is that the outgoing terrestrial radiation has a systematic diurnal cycle. Currently, the outgoing terrestrial radiation is sampled from the so-called morning and afternoon Sun-synchronous orbits, complemented by narrow band geostationary imagers. Recently the sampling from the morning orbit was abandoned. The sampling of the diurnal cycle can be improved, for example, by using two orthogonal 90° inclined orbits which give both global coverage, and a statistical sampling of the full diurnal cycle at seasonal time scale. For understanding the radiative forcing – e.g. aerosol radiative forcing - and climate feedback – e.g. ice albedo feedback - mechanisms underlying changes in the EEI, and for climate model validation, it is necessary to separate the Total Outgoing Radiation (TOR) spectrally into the two components of the Earth Radiation Budget (ERB), namely the Reflected Solar radiation (RSR) and Outgoing Longwave Radiation (OLR) and to map them at relatively high spatial resolution. The Earth Climate Observatory (ECO) mission concept was recently selected by the European Space Agency as one of the 4 candidate Earth Explorer 12 missions, that will be further studied in Phase 0 until mid 2026. The current paper provides a broad overview of the ECO mission objectives, the mission requirements, and the key elements of a baseline mission concept. During Phase 0, the ECO mission concept will be further elaborated in two parallel industrial studies, which may or may not adopt or refine the elements of the baseline concept.

Space-based spectrometers are of high importance for Earth observation and greenhouse gas sensing. We present a novel freeform pushbroom imaging spectrometer, covering the visible (400 - 1100 nm), near-infrared (1100 - 1700 nm) and thermal (8 - 14 mu m) wavelength range, showing a full field-of-view of 120 degrees, while fitting within a single CubeSat Unit. The design is composed of a freeform 2-mirror telescope, followed by a freeform spectrometer unit. The freeform telescope guides the light to the spectrometer entrance slit, after which a collimating mirror is present, and the light is split to the 3 spectrometer channels. Each spectrometer channel focuses the light onto a 2D detector providing both spatial and spectral information. The visible spectrometer channel comprises a transmission diffraction grating followed by 2 freeform mirrors, enabling a nadir spatial resolution of 9.87 km and a spectral resolution of 5.18 nm. The near-infrared and thermal spectrometer each comprise a reflective diffraction grating and 2 freeform mirrors, featuring a nadir spatial resolution of 4.13 km and 9.31 km, and a spectral resolution of 2.74 nm and 48.27 nm, respectively. All mirrors are described using XY polynomials, up to the 4th order, enabling a close to diffraction-limited performance. Consequently, this design might benefit future space missions enabling an improved Earth observation and climate monitoring.

The Earth Energy Imbalance (EEI) is defined as the small difference between the incoming energy received by the Earth from the Sun and the outgoing energy lost by the Earth to space. Both the incoming solar and the terrestrial outgoing energy are of the order of 340 W/m² at the global annual mean level, while the EEI is of the order of 0.9 W/m². The EEI is accumulated in the Earth’s climate system, particularly in the oceans which have a high heat capacity, and results in global temperature rise. Despite its fundamental importance, the EEI is currently poorly measured from space, due to two fundamental challenges. A new space mission concept, called the Earth Climate Observatory (ECO) - with as primary mission objective the accurate and stable monitoring of the EEI - is currently elaborated. The first fundamental challenge is that the EEI is the relatively small difference between two opposite terms with large and nearly equal amplitude. Currently, incoming solar radiation and outgoing terrestrial radiation are measured with separate instruments, which means that their calibration errors are added, and overwhelm the signal to be measured. In order to make significant progress in this challenge, a differential measurement using identically designed, intercalibrated instruments—so-called wide-field-of-view (WFOV) radiometers—to measure both the incoming solar radiation and the outgoing terrestrial radiation is needed. The second fundamental challenge is that the outgoing terrestrial radiation has a systematic diurnal cycle. An adequate sampling of the global diurnal cycle can be obtained by using an innovative constellation of two orthogonal 90° inclined orbits which provide both global coverage and a statistical sampling of the full diurnal cycle at the seasonal (3-month) time scale. The wide-field-of-view radiometer will make accurate low-spatial-resolution measurements of the Total Outgoing Radiation (TOR) of the Earth. Auxiliary innovative multispectral visible and thermal imagers – with high information content, serving a multitude of possible secondary mission objectives - will be used to increase the spatial resolution of the radiometer observations and to separate the TOR spectrally in the Reflected Solar Radiation (RSR) and the Outgoing Longwave Radiation (OLR).

Earth observation and greenhouse gas sensing from space provides vital information for climate and climate change monitoring, indicating the importance of novel spaceborne telescopes and spectrometers. We present a novel freeform pushbroom imaging spectrometer enabling the sensing of water vapor, carbon dioxide and methane in the atmosphere, while fitting within 2 CubeSats Units. The design comprises a 2-mirror freeform telescope, combined with a near-infrared (1100 – 1700 nm) spectrometer featuring 3 freeform mirrors and a reflective grating, providing both spatial and spectral information using a 2D detector. All mirrors are described and optimized using XY polynomials, enabling a nearly diffraction-limited performance. The novel design is exceeding the state-of-the-art, by showing a full FOV of 120°, a spatial resolution of 2.6 km, and a spectral resolution of 13 nm. According to our knowledge, our novel design shows the widest field-of-view that has ever been realized for space-based telescopes, nearly reaching Earth observation from limb to limb from an altitude of about 700 km. The freeform telescope mirrors were manufactured in-house using high-precision 5-axis milling and 5-axis ultraprecision diamond tooling. Finally, a laboratory proof-of-concept demonstrator was realized validating the field-of-view and focusing spot sizes, paving the way for future space missions that target wide field-ofview imaging and/or an enhanced climate monitoring.

As part of the Earth Climate Observatory space mission concept for the direct observation from space of the Earth Energy Imbalance, we propose an advanced camera suite for the high-resolution observation of the Total Outgoing Radiation of the Earth. For the observation of the Reflected Solar Radiation, we propose the use of two multispectral cameras covering the range from 400 to 950 nm, with a nadir resolution of 1.7 km, combined with a high-resolution RGB camera, with a nadir resolution of 0.57 km. For the observation of the Outgoing Longwave Radiation, we propose the use of six microbolometer cameras, with each a spectral bandwidth of 1 μm in the range from 8 to 14 μm, with a nadir resolution of 2.2 km.

Observing the Earth radiation budget (ERB) at top of the atmosphere (TOA) from space is crucial for monitoring and understanding Earth’s climate. The accurate estimation of Earth’s outgoing radiative flux is of critical importance to studying ERB at TOA. The Moon-based wide field-of-view radiometer (MWFVR) can provide long-term, continuous full-disk broadband irradiance measurements, which provides an important data source for studying the ERB. Within this context, the lunar surface site 0° E 0° N is selected as the position of the Moon-based wide field-view radiometer, and based on the radiation transfer function, the entrance pupil irradiances time series are obtained by utilization of the CER_SYN1deg-1Hour_Edition4 data products and ERBE ADMs, which is used as the substitute for the truth of the measurements. In this work, the Earth outgoing radiative flux estimating model from the MWFVR measurements is established, and according to the framework, the entrance pupil irradiances are converted to full-disk LW and daytime SW outgoing radiative fluxes. By comparing the results from Moon-based radiometer measurements with those from NISTAR data and CERES SYN1deg data, the results show the moon-based data a much better agreement with those from the satellite data. Besides, The Moon-based SW fluxes oscillate around 194 and 205 W∙m-2, and the range of LW fluxes is 251 ~ 287 Wm−2. Therefore, the complementary advantages and cooperative work of platforms at different altitudes will be an important way for future research on the ERB.

A Moon-based radiometer can provide continuous measurements for the Earth’s full-disk broadband irradiance, which is useful for studying the Earth’s Radiation Budget (ERB) at the height of the Top of the Atmosphere (TOA). The ERB describes how the Earth obtains solar energy and emits energy to space through the outgoing broadband Short-Wave (SW) and emitted thermal Long-Wave (LW) radiation. In this work, a model for estimating the Earth’s outgoing radiative flux from the measurements of a Moon-based radiometer is established. Using the model, the full-disk LW and SW outgoing radiative flux are gained by converting the unfiltered entrance pupil irradiances (EPIs) with the help of the anisotropic characteristics of the radiances. Based on the radiative transfer equation, the unfiltered EPI time series is used to validate the established model. By comparing the simulations for a Moon-based radiometer with the satellite-based data from the National Institute of Standards and Technology Advanced Radiometer (NISTAR) and the Clouds and the Earth’s Radiant Energy System (CERES) datasets, the simulations show that the daytime SW fluxes from the Moon-based measurements are expected to vary between 194 and 205 Wm−2; these simulations agree well with the CERES data. The simulations are about 5 to 20 Wm−2 smaller than the NISTAR data. For the simulated Moon-based LW fluxes, the range is 251~287 Wm−2. The Moon-based and NISTAR fluxes are consistently 5~15 Wm−2 greater than CERES LW fluxes, and both of them also show larger diurnal variations compared with the CERES fluxes. The correlation coefficients of SW fluxes for Moon-based data and NISTAR data are 0.97, 0.63, and 0.53 for the months of July, August, and September, respectively. Compared with the SW flux, the correlation of LW fluxes is more stable for the same period and the correlation coefficients are 0.87, 0.69, and 0.61 for July to September 2017.

The long term global temperature rise caused by increased greenhouse gas radiative forcing is partially masked by temporary aerosol radiative cooling, which remains poorly known.I present a new purely observation based estimate of Aerosol Radiative Forcing (ARF) due solely to the direct radiative effect of aerosols over clear sky ocean, and its time variation over the period 2003-20204 from combined MODIS and CERES aerosol, cloud, and radiation measurements. The resulting mean 2003-2020 ARF is -1.16 +/- 0.39 W/m2 , with no significant trend within an uncertainty of +/- 0.025 W/m2dec.Combining this ARF with the best estimate of the greenhouse gas and solar radiative forcing, and the most likely value of the Equilibrium Climate Sensitivity, produces a plausible Earth Energy Imbalance as a residual of the energy balance equation at the top of the atmosphere.

Moon-Based Earth Radiation Observation (MERO) is expected to improve and enrich the current Earth radiation budget (ERB). For the design of MERO’s instrument and the interpretation of Moon-based data, evaluating the uncertainty of the instrument’s Entrance Pupil Irradiance (EPI) is an important part. In this work, by analyzing the effect of the Angular Distribution Models (ADMs), Earth’s Top of Atmosphere (TOA) flux, and the Earth–Moon distance on the EPI, the uncertainty of EPI is finally studied with the help of the theory of errors. Results show that the ADMs have a stronger influence on the Short-Wave (SW) EPI than those from the Long-Wave (LW). For the change of TOA flux, the SW EPI could keep the attribute of varying hourly time scales, but the LW EPI will lose its hourly-scale variability. The variation in EPI caused by the hourly change of the Moon–Earth distance does not exceed 0.13 mW∙m−2 (1σ). The maximum hourly combined uncertainty reveals that the SW and LW combined uncertainties are about 5.18 and 1.08 mW∙m−2 (1σ), respectively. The linear trend extraction of the EPI demonstrates that the Moon-based data can effectively capture the overall linear change trend of Earth’s SW and LW outgoing radiation, and the uncertainty does not change the linear trend of data. The variation of SW and LW EPIs in the long term are 0.16 mW∙m−2 (SW) and 0.23 mW∙m−2 (LW) per decade, respectively. Based on the constraint of the uncertainty, a simplified dynamic response model is built for the cavity radiometer, a kind of MERO instrument, and the results illuminate that the Cassegrain optical system and electrical substitution principle can realize the detection of Earth’s outing radiation with the sensitivity design goal 1 mW∙m−2.

Wide field-of-view imaging optics offers a huge potential for space-based Earth observation and climate change monitoring by capturing global data. We present the design and proof-of-concept demonstration of a freeform 2-mirror space-based telescope featuring a full field-of-view of 120°, nearly reaching Earth observation from limb to limb from a nominal altitude of 700 km, while showing a spatial resolution of 2.6 km, and fitting within 1 CubeSat unit. Our design benefits from freeform optics to maximize the field-of-view, while maintaining a diffraction-limited image quality and minimizing the system dimensions. Particularly, both mirror surfaces were accurately modelled and optimized using an XY polynomial description. Subsequently, the mirrors are manufactured using high-precision 5-axis milling and ultraprecision diamond tooling, after which a laboratory demonstrator setup of the telescope was realized. We believe this design paves the way towards future space missions enabling an improved Earth observation, leading to an enhanced monitoring of climate and climate change.

<p>Monitoring the Earth Radiation Budget (ERB) and in particular the Earth<br>Energy Imbalance (EEI), is of paramount importance for a predictive<br>understanding of global climate change.   We propose the new Earth<br>Climate Observatory (ECO) space mission concept for the monitoring of<br>the EEI.<br><br>The EEI is defined as the small difference between the two nearly equal<br>terms of the incoming solar radiation, and the outgoing terrestrial<br>radiation lost to space. Making a significant measurement of the EEI<br>from space is very challenging, and requires a differential measurement<br>with one single instrument of both the incoming solar radiation and the<br>outgoing terrestrial radiation. The instrument that allows such a<br>differential measurement is an improved wide field of view electrical<br>substitution cavity radiometer.<br><br>The wide field of view radiometer will observe the earth from limb to<br>limb. A single measurement footprint is a circle with a diameter around<br>6300 km. For the discrimination of cloudy and clear skies, a higher<br>spatial resolution is needed. This will be obtained from two wide field<br>of view cameras, a visible wide field of view camera for the<br>characterisation of the spatial distribution of the reflected solar<br>radiation, and a thermal infrared wide field of view camera for the<br>characterisation of the spatial distribution of the emitted thermal<br>radiation.</p>

We report on a near-infrared imaging spectrometer for sensing the three most prominent greenhouse gases in the atmosphere (water vapor, carbon dioxide and methane). The optical design of the spectrometer involves freeform optics, which enables achieving exceptional performance and allows progressing well beyond the state-of-the-art in terms of compactness, field-of-view, and spatial resolution. The spectrometer is intended to be launched on a small satellite orbiting at 700 km and observing the Earth with a wide field-of-view of 120° and a spatial resolution of 2.6 km at nadir. The satellite will ultimately allow for improved climate change monitoring.

In July 2021, western Europe has been subject to extreme rainfall that lead to severe flooding, incurring heavy property losses and claiming dozens of people’s lives in both Germany and Belgium. This unfortunate disaster is a reminder that carrying out studies about extreme event forecasting is a matter of prime importance in the field of meteorology. The extreme rainfall from July 2021 invites us to study the performance of our deep learning method for precipitation estimation in case of extreme events. The main novelty of our method resides in its ability to merge different physical measurement modalities in order to improve precipitation estimation accuracy. In specific, the proposed method merges rain gauge measurements with a ground-based radar composite and thermal infrared satellite imagery. The proposed convolutional neural network design, composed of an encoder–decoder architecture, performs multiscale analysis of the three input modalities to simultaneously estimate the rainfall probability and the precipitation rate with a spatial resolution of 2 km. The training of our model and its performance evaluation are carried out on a dataset spanning 5 years from 2015 to 2019 and covering Belgium, the Netherlands, Germany and the North Sea. Once trained, we evaluate the performance of our model to estimate the extreme precipitation that happened in Belgium and Germany in July 2021 by comparing our results with the measurements from rain gauges and radar estimation.

Climate change monitoring is still a major challenge, which is currently typically addressed using radiometers monitoring the radiative fluxes at the top of the atmosphere. To improve the current state-of-the-art monitoring instruments, we pursue the development of novel space instrumentation, combining a radiometer with two additional imagers, improving the spatial resolution to a few kilometers allowing scene identification, while enabling a spectral distinction between the reflected solar radiation (RSR) using a visible to near-infrared (400 – 1100 nm) camera, and the Earth’s emitted thermal radiation using a thermal infrared (8 – 14 μm) camera. In this paper, we present a novel camera design optimized towards RSR monitoring, while targeting a compact design and minimizing the number of aspheric components. More specifically, our optimized imaging design shows a wide field of view (138°) enabling to observe the Earth from limb to limb, a compact volume fitting within 1 CubeSat Unit (1U), a wide spectral range (400 – 900 nm) to retrieve the RSR with a certainty of more than 95%, a spatial resolution better than 5 km at nadir, and a close to diffraction-limited performance. After optimization towards the nominal design, possible design alternatives are considered and discussed, enabling a cost-efficient design choice. Following, the mechanical and optical design tolerances are evaluated using a statistical Monte Carlo analysis, indicating a robust and tolerant design that can be manufactured using ultra-precision diamond tooling. Finally, stray-light analysis was performed enabling evaluation of ghost reflection and evaluating the necessity of an anti-reflection coating. Consequently, we can conclude our proposed imaging designs show a promising performance optimized towards Earth observation, paving the way to an improved climate change monitoring.

Total Solar Irradiance (TSI) quantifies the solar energy received by the Earth and therefore is of direct relevance for a possible solar influence on climate change on Earth. We analyse the TSI space measurements from 1991 to 2021, and we derive a regression model that reproduces the measured daily TSI variations with a Root Mean Square Error (RMSE) of 0.17 W/m2. The daily TSI regression model uses the MgII core to wing ratio as a facular brightening proxy and the Photometric Sunspot Index (PSI) as a measure of sunspot darkening. We reconstruct the annual mean TSI backwards to 1700 based on the Sunspot Number (SN), calibrated on the space measurements with an RMSE of 0.086 W/m2. The analysis of the 11 year running mean TSI reconstruction confirms the existence of a 105 year Gleissberg cycle. The TSI level of the current grand minimum is only about 0.15 W/m2 higher than the TSI level of the grand minimum in the beginning of the 18th century.

Wide field-of-view imaging optics offer a huge potential for space-based Earth observation enabling the capture of global data. Reflective imaging telescopes are often favored, as they do not show chromatic aberrations and are less susceptible to radiation darkening than their refractive counterparts. However, the main drawback of reflective telescopes is that they are limited with respect to field-of-view while featuring large dimensions. We propose the use of freeform optics to maximize the field of view while maintaining diffraction-limited image quality and minimizing system dimensions. In this paper, we present a novel freeform wide field-of-view reflective telescope, starting from the optical design, and continuing to tolerancing analysis and manufacture, towards a proof-of-concept demonstrator. The novel telescope features a full field-of-view of 120° while showing an exceptional spatial resolution of 2.6 km and fitting within 1 CubeSat unit. To the best of our knowledge, this is the widest field-of-view that has ever been realized for a space-based telescope, nearly reaching Earth observation from limb to limb from an altitude of about 700 km. We hope this design paves the way for future space missions enabling improved Earth observation and leading to enhanced monitoring of climate and climate change.

To improve precipitation estimation accuracy, new methods, which are able to merge different precipitation measurement modalities, are necessary. In this study, we propose a deep learning method to merge rain gauge measurements with a ground-based radar composite and thermal infrared satellite imagery. The proposed convolutional neural network, composed of an encoder–decoder architecture, performs a multiscale analysis of the three input modalities to estimate simultaneously the rainfall probability and the precipitation rate value with a spatial resolution of 2 km. The training of our model and its performance evaluation are carried out on a dataset spanning 5 years from 2015 to 2019 and covering Belgium, the Netherlands, Germany and the North Sea. Our results for instantaneous precipitation detection, instantaneous precipitation rate estimation, and for daily rainfall accumulation estimation show that the best accuracy is obtained for the model combining all three modalities. The ablation study, done to compare every possible combination of the three modalities, shows that the combination of rain gauges measurements with radar data allows for a considerable increase in the accuracy of the precipitation estimation, and the addition of satellite imagery provides precipitation estimates where rain gauge and radar coverage are lacking. We also show that our multi-modal model significantly improves performance compared to the European radar composite product provided by OPERA and the quasi gauge-adjusted radar product RADOLAN provided by the DWD for precipitation rate estimation.