In situ registrations of electron density from the Langmuir probe on board Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions satellite are used to study spatial and temporal evolution of nighttime plasma density enhancements (NPDEs). The study introduces the normalized density difference index I NDD in order to provide global estimates of the phenomenon. In the validation test, in situ data are compared with synthetic data set generated with the International Reference Ionosphere model. We find signatures of two most common examples of NPDEs, the Weddell Sea Anomaly (WSA) and midlatitude nighttime summer anomaly (MSNA) with proposed index, in the topside ionosphere. The study provides evidence that the occurrence of the WSA and MSNA is not limited to the local summer conditions. Analyzed annual trend of I NDD and in particular spatial pattern obtained during equinoxes suggest that mechanisms governing the behavior of the equatorial ionosphere cannot be neglected in the explanation of the development of NPDEs.
The paper tries interpreting how the method of SMOS observations realizes managing the problem of large scales and the target heterogeneity by means of employing the polarization angular signature. Land surface target on the Earth is naturally heterogeneous in its continuity of physical and biophysical properties. Soil moisture (SM) retrieval from SMOS data requires using the model CMEM to determine relations between the temperature brightness and water related properties and conditions, which are anchored to the ground by auxiliary data. SM retrieval must start from the conditions at least approaching physical reality. SMOS performs the data fusion in NRT (Nearly Real Time) in a very specific way, what is a new quality added to EO (Earth Observations). The paper demonstrates several effects of employing the SM retrievals from L1C data. Authors explain how they validate few selected test sites in Poland, and come to conclusions on choosing a strategy focused on validating single sites. Finally, they come to an understanding that SM retrieval is an advanced statistical method requiring good referencing to ground based physical conditions in large scales, worth confronting the shallow water content obtained from SMOS to that assessments of the total water content on continental scales, which available from effects of gravitational missions
International audienceDEMETER was a low Earth orbiting microsatellite in operation between July 2004 and December 2010. Its scientific objective was the study of ionospheric perturbations in relation to seismic activity and man-made activities. Its payload was designed to measure electromagnetic waves over a large frequency range as well as ionospheric plasma parameters (electron and ion densities, fluxes of energetic charged particles). This paper will show both expected and unusual events recorded by the satellite when it was in operation. These latter events have been selected from the DEMETER database because they are rare or even have never been observed before, because they have a very high intensity, or because they are related to abnormalities of the experiments under particular plasma conditions. Some events are related to man-made radio waves emitted by VLF ground-based transmitters or power line harmonic radiation. Natural waves, such as atypical quasi-periodic emissions or uncommon whistlers, are also shown
Artificial sources emitting in the protected part of the L-band are contaminating the retrievals of the soil moisture and ocean salinity (SMOS) satellite launched by the European Space Agency (ESA) in November 2009. Detecting and pinpointing such sources is crucial for the improvement of SMOS science products as well as for the identification of the emitters.In this contribution, we present a method to obtain snapshotwise information about sources of radio-frequency interference (RFI). The localization accuracy of this method is also assessed for observed RFI sources. We also show that RFI localizations constitute a useful data set for assessing the pointing performance of the satellite, and present how it is possible, using the results of this method, to identify and estimate two systematic errors in the geo-location of the satellite field of view. The potential causes and the approaches to mitigate both these errors are discussed.Index Terms-Ascending-descending bias, detection, localization, radio-frequency interference (RFI), soil moisture and ocean salinity (SMOS), systematic error.
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