The Ionospheric Anomaly Monitoring by Magnetometer And Plasma-probe (IAMMAP) is one of the scientific instruments for the Compact Advanced Satellite 500-3 (CAS 500-3) which is planned to be launched by Korean Space Launch Vehicle in 2024. The main scientific objective of IAMMAP is to understand the complicated correlation between the equatorial electro-jet (EEJ) and the equatorial ionization anomaly (EIA) which play important roles in the dynamics of the ionospheric plasma in the dayside equator region. IAMMAP consists of an impedance probe (IP) for precise plasma measurement and magnetometers for EEJ current estimation. The designated sun-synchronous orbit along the quasi-meridional plane makes the instrument suitable for studying the EIA and EEJ. The newly-devised IP is expected to obtain the electron density of the ionosphere with unprecedented precision by measuring the upper-hybrid frequency (fUHR) of the ionospheric plasma, which is not affected by the satellite geometry, the spacecraft potential, or contamination unlike conventional Langmuir probes. A set of temperaturetolerant precision fluxgate magnetometers, called Adaptive In-phase MAGnetometer, is employed also for studying the complicated current system in the ionosphere and magnetosphere, which is particularly related with the EEJ caused by the potential difference along the zonal direction.

This paper describes the initial operations and preliminary results of the Instrument for the study of Stable/Storm-time Space (ISSS) onboard the microsatellite Next Generation Small Satellite-1 (NEXTSat-1), which was launched on December 4, 2018 into a sun-synchronous orbit at an altitude of 575 km with an orbital inclination angle of 97.7°. The spacecraft and the instruments have been working normally, and the results from the observations are in agreement with those from other satellites. Nevertheless, improvement in both the spacecraft/instrument operation and the analysis is suggested to produce more fruitful scientific results from the satellite operations. It is expected that the ISSS observations will become the main mission of the NEXTSat-1 at the end of 2020, when the technological experiments and astronomical observations terminate after two years of operation.

This paper describes a computation method for obtaining dielectric constant using Global Navigation Satellite System reflectometry (GNSS-R) products. Dielectric constant is a crucial component in the soil moisture retrieval process using reflected GNSS signals. The reflectivity for circular polarized signals is combined with the dielectric constant equation that is used for radiometer observations. Data from the Cyclone Global Navigation Satellite System (CYGNSS) mission, an eight-nanosatellite constellation for GNSS-R, are used for computing dielectric constant. Data from the Soil Moisture Active Passive (SMAP) mission are used to measure the soil moisture through its radiometer, and they are considered as a reference to confirm the accuracy of the new dielectric constant calculation method. The analyzed locations have been chosen that correspond to sites used for the calibration and validation of the SMAP soil moisture product using in-situ measurement data. The retrieved results, especially in the case of a specular point around Yanco, Australia, show that the estimated results track closely to the soil moisture results, and the Root Mean Square Error (RMSE) in the estimated dielectric constant is approximately 5.73. Similar results can be obtained when the specular point is located near the Texas Soil Moisture Network (TxSON), USA. These results indicate that the analysis procedure is well-defined, and it lays the foundation for obtaining quantitative soil moisture content using the GNSS reflectometry results. Future work will include applying the computation product to determine the characteristics that will allow for the separation of coherent and incoherent signals in delay Doppler maps, as well as to develop local soil moisture models.

In this paper, we present observations of the Space Radiation Detectors (SRDs) onboard the Next Generation Small Satellite-1 (NEXTSat-1) satellite. The SRDs, which are a part of the Instruments for the study of Stable/Storm-time Space (ISSS), consist of the Medium-Energy Particle Detector (MEPD) and the High-Energy Particle Detector (HEPD). The MEPD can detect electrons, ions, and neutrals with energies ranging from 20 to 400 keV, and the HEPD can detect electrons over an energy range from 0.35 to 2 MeV. In this paper, we report an event where particle flux enhancements due to substorm injections are clearly identified in the MEPD A observations at energies of tens of keV. Additionally, we report a specific example observation of the electron distributions over a wide energy range in which we identify electron spatial distributions with energies of tens to hundreds of keV from the MEPD and with energy ranging up to a few MeV from the HEPD in the slot region and outer radiation belts. In addition, for an ~1.5-year period, we confirm that the HEPD successfully observed the well-known outer radiation belt electron flux distributions and their variations in time and L shell in a way consistent with the geomagnetic disturbance levels. Last, we find that the inner edge of the outer radiation belt is mostly coincident with the plasmapause locations in L, somewhat more consistent at subrelativistic energies than at relativistic energies. Based on these example events, we conclude that the SRD observations are of reliable quality, so they are useful for understanding the dynamics of the inner magnetosphere, including substorms and radiation belt variations.

Dielectric constant describes the electrical properties of a material and is related to soil moisture. The latter is known as a critical parameter in hydrological and climate science; however, computing such dielectric constants is a challenging problem as many factors effect the constant values, e.g., soil type, texture and temperature. Global Navigation Satellite System-Reflectometry (GNSS-R) is a relatively new remote sensing technique being used to infer geophysical information by measuring not only the signals coming directly from the GNSS satellites, but also the reflected GNSS signals from the Earth’s surface. This research presents a new, straightforward approach for computing relative dielectric constant by means of reflectivity, which is the ratio between the signal-to-noise ratio (SNR) of direct waves and SNR of reflected waves. With the well-known relationship between the reflectivity, Fresnel coefficient, and surface roughness, the dielectric constant can be expressed as the combination of horizontal and vertical Fresnel coefficients. Dual, circular-polarized antennas in the zenith and nadir directions were used to capture electromagnetic waves emitted from GNSS satellites and transform them into electrical signals. The zenith direction antenna senses the direct signals which have right-hand circular polarization, and the nadir direction antenna senses right and left-hand circular polarization of reflected GNSS signals created by electromagnetic reflections on the surfaces. An in-house Software Defined Radio (SDR) receiver, coupled with a commercial radio frequency frontend were used to collect, store and analyze both direct and reflected signals. Data collection experiments were carried in areas of smooth surface, and the observed SNR values were applied to the method of quantitative dielectric constant. The computation results demonstrate that derived dielectric constants have the values around 10 and are independent on the incident angle of waves coming to the specular point. Applying the additional data processing to the results, it is relevant to the dielectric constant measured by Time Domain Reflectometry techniques used commercial soil moisture probes at the same time. There have been few attempts to establish the dielectric constant model using forward scattered electromagnetic signals, especially GNSS signals. The proposed calculation method is able to solve the difficulties in analyzing with respect to the incident angle, as well as the polarization. Therefore, it is expected that the inversion approach of the retrieval algorithm makes the GNSS-R applicable to not only the scientific but also the industrial applications. In the future, the dielectric constant will be enhanced to include roughness information of the Earth’s surface and to attempt to calibrate surface soil moisture measurements for various soil types.