RUAG (Sweden)

<strong class="journal-contentHeaderColor">Abstract.</strong> The back propagation (BP) method consists of diffractive integrals computed over a trajectory path, projecting a signal to different planes. It unwinds the diffraction and multipath, resulting in minimum disturbance on the BP amplitude when the auxiliary plane coincides with the region causing the diffraction. The method has been previously applied in GNSS Radio Occultation (RO) measurements showing promising results in the location estimate of ionospheric irregularities but without complementary data to validate the estimation. In this study, we investigate with wave optics propagator (WOP) simulations of an equatorial C/NOFS occultation with scintillation signatures caused by an equatorial plasma bubble (EPB), which was parametrized with aid of collocated data. In addition, a few more test cases were designed to assess the BP method regarding size, intensity and placement of single and multiple irregularity regions. The results show a location estimate accuracy of 10 km (single bubble, reference case), where in multiple bubble scenarios only the strongest disturbance would be resolved properly. The minimum detectable disturbance level and the estimation accuracy depend on the receiver noise level, and in the case of several bubbles on the distance between them. The remarks of the evaluation supported the interpretation of results for two COSMIC occultations.

Wave optics propagators (WOPs) are commonly used to describe the propagation of radio signals through earth's atmosphere. In radio occultation (RO) context, multiple phase screen (MPS) method has been used to model the effects of the atmosphere in Global Navigation Satellite System (GNSS) signals during an occultation event. WOP implementation includes, in addition to MPS, a diffraction integral as the final step to calculate the radio signal measured in the low-earth orbit (LEO) satellite. This approach considers vacuum as the propagation medium at high altitudes, which is not always the case when the ionosphere is taken into account in simulations. An alternative approach is using MPS all the way to LEO in order to sample the GNSS signal in orbit. This approach, named MPS orbit sampling (MPS-OS), is evaluated in this letter. Different scenarios of setting occultation assuming a short segment of the LEO orbit have been simulated using MPS and MPS-OS. Results have been compared to Abel transform references. Furthermore, a long segment scenario has been evaluated as well. A comparison of bending angle (BA) and residual ionospheric error (RIE) shows the equivalence between MPS and MPS-OS results. The main application of MPS-OS should be in occultation events with long segments of orbit and including ionosphere, in which a standard WOP may not be appropriate.

Radio Occultation based on Global Navigation Satellite System signals (GNSS RO) is an increasingly important remote sensing technique. Its measurements are used to derive parameter of the Earth's atmosphere, e.g., pressure, temperature and humidity, with good accuracy. The systematic residual error present on the data processing is related to ionospheric conditions, such as the distribution of electrons and the resultant vertical gradient. This study investigates the relationship between these parameters and the residual ionospheric error (RIE) on the retrieved bending angle in the stratosphere. Chapman function combined to sinusoidal perturbations are used to model electron density profiles and compared to RO retrievals of the ionosphere to perform the investigation. The results confirmed that the major ionospheric influence on the retrieval error is related to the F-layer electron density peak, whereas small-scale vertical structures play a minor role.

The next generation GNSS radio occultation instrument under development at RUAG Space will take advantage of the new signals of Galileo, GPS, GLONASS, and Compass. The measurement performance is improved as compared to the present instrument generation that operates on the MetOp satellites. A tracking algorithm has been developed which ensures that all signal information throughout the atmosphere is made available for ground processing with a minimum of losses. Simulation results are presented for a demanding case of a rising occultation.

This chapter presents an overview of the development of various antennas for small-satellite applications. It gives an introduction to small satellites at the beginning and introduces different types of small satellites. The chapter discusses challenges for designing antennas for small satellite. It discusses many small satellite antennas for TTC, data downlink, GNSS and intersatellite links such as patch antennas, the PEC antenna, QHA, horn antennas, and so on. The chapter finally provides two real-world case studies which illustrate the practical design and development of antennas for small satellites. The future development of antennas for small satellites will move towards higher frequencies, electronic beam steering and multiple functions as well as smaller size. Controlled Vocabulary Terms antennas; beam steering; horn antennas; Perfect electrical conductor antenna; satellite links; satellite navigation

We present a promising application of the inverse source technique for antenna diagnostics and the creation of a synthetic higher-performance measurement environment. The focus is on the post-processing of antenna measurements via the recently introduced dual-equation formulation of the inverse source problem, which provides the equivalent sources with highest correlation to actual radiators among the infinite possible choices of equivalence. It is shown how, in practically relevant conditions, measured data can be spatially filtered in the source domain to recover reference conditions not achievable during measurements, e.g., perfectly balanced antenna feeding and absence of supporting structure. The procedure proposed is useful also in the detection, synthetic elimination, and actual correction of the effect of undesired interactions with scatterers in the measurement volume, such as the supporting platform and surrounding obstacles.