NGRM – Next Generation Radiation Monitor on EDRS-C
NGRM is the second Space Weather instrument flying as part of ESA’s Distributed Space weather Sensor System (D3S). It is hosted on the European Data Relay System - C (EDRS-C) spacecraft, located in GEO at 31° East.
Figure 1. Illustration of ESA’s Distributed Space Weather Sensor System concept planned to be realised through hosted payload missions as well as dedicated small satellite missions.
NGRM entails two particle sensors, the electron detector (ED) consisting of 16 circular silicon strip detectors with a circular step collimator on top, and the stacked detector (SD) comprising an assembly of seven silicon detectors layered with several aluminum and tantalum degraders. Incident charged particles are registered according to the detection logic in one of 16 electron or one of 10 proton channels. [L. Desorgher et al., 2013]
Figure 2. The NGRM flight model with the detector system in the right of the instrument and the data handling and I/F electronics in the left part
ED and SD have been calibrated with both experimental and numerical means. The electron (proton) response functions (RF) of ED and SD have been derived using 4π-and linear-beam GEANT4 simulations slightly re-adjusted with experimental results based on the unit’s experimental calibrations at the Proton Irradiation and the Electron Monochromator Facilities at Paul Scherrer Institute, Switzerland.
Figure 3. Model of the NGRM electron detector (left) and stacked detector (right).
For the calculation of electron and flux products, two different methods have been applied; the Bow-Tie (BT) analysis and the Genetic Correlative Unfolding Method (GenCORUM).
The BT analysis applies to the response functions of the detectors channels and allows the derivation of a scaling factor for the conversion of the detector’s count rates to flux products for an energy value that minimizes the uncertainties expected at the encountered space radiation environment (cf. Sandberg et al 2019)
The GenCORUM [Aminalragia-Giamini et. al 2018] is an artificial intelligence method which employs a Cased-Based Reasoning (CBR) process coupled with a Genetic Algorithm (GA). The CBR process performs an initial crude unfolding taking into account the count-rates measured from all the detector channels simultaneously, and the GA optimizes the resulted flux values.
The current data release of EDRS-C/NGRM flux Level 1 datasets consists of
which includes proton omnidirectional differential fluxes FPDO[ (cm2 s sr MeV)-1 ] and integral fluxes FEIO[ (cm2 s sr)-1] estimated using simple geometric factors derived with a BT method, and the
which includes electron omnidirectional differential fluxes FEDO[ (cm2 s sr MeV)-1 ] de-convoluted using the GenCORUM. The energy bins and the respective energies [MeV] per particle and spectra type of the provided datasets are given in Table 1
The datasets include also timestamps, ephemeris data (in the ECI coordinate system) and magnetic coordinates (L, L*, MLT etc). The magnetic coordinates were derived using the UNILIB library (accessible here) assuming the IGRF model for the internal, and the quiet Olson-Pfitzer 1977 model for the external magnetic field components.
For more details on the EDRS-C/NGRM data sets, please consult the Data Description Document