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Metal cesium (Cs) vapor, released at an altitude in the upper atmosphere, generates an artificial space plasma cloud with high electron density. It can act as a scatter to realize radio communication across an over-the-horizon distance. A full-life model of radio propagation via an artificial plasma cloud is established based on its space–time evolution in this article. In addition, this model is verified by the sounding data of the rocket release experiment carried out in the United States. The multipath effect of plasma cloud scattering is studied by using ray tracing, and then, the coherent bandwidth is estimated for this spatial channel. Also, the theoretical channel model of artificial plasma cloud is established by using its space–time evolution and atmospheric wind field parameters. Considering common modulation modes and receiver noise levels, the potential communication performance is evaluated by using the proposed channel model, such as the transmission rate, the bit error rate (BER), and the available time for building up and maintaining communication links. It is shown that the maximal communication rate is up to 200 kb/s, BER overall maintains below 10−7, and the available time for a single release is about 30–60 min; for the case of this article, they are release mass of 2–10 kg, communication distances of 400–1200 km, and radio frequencies of 30–70 MHz at the VHF band. This demonstrates that the artificial channel can propagate radio waves at a much higher frequency, wider bandwidth, and higher rate than those of HF communication. Hopefully, it could be a solution to overcome the intolerable shortcoming and adverse effects on HF communication due to ionospheric disturbances especially in cases of maritime, emergency, and minimum communications [ABSTRACT FROM AUTHOR]

Implementation of the Federal Communications Commission's (FCC) E-911 Phase-2 requirements and commercial location-based services in urban environments requires mobile station (MS) localization capabilities in non-line-of-sight (NLOS) propagation conditions. This work addresses the problem of MS localization in urban environments characterized by the NLOS propagation conditions and limited Global Positioning System (GPS) services. We propose a single-base-station-based localization approach that uses a statistical model of urban propagation conditions in the framework of target classification. The proposed localization approach involves no data collection during the training process, requires no modifications of the MS hardware, is not location specific, and requires no identification and mitigation of the NLOS conditions. The performance of the proposed localization approach was evaluated using collected and ray-traced measurements. [ABSTRACT FROM PUBLISHER]

We have developed an algorithm to retrieve scattering cloud pressures and other cloud properties with the Aura Ozone Monitoring Instrument (OMI). The scattering cloud pressure is retrieved using the effects of rotational Raman scattering (RRS). It is defined as the pressure of a Lambertian surface that would produce the observed amount of RRS consistent with the derived reflectivity of that surface. The independent pixel approximation is used in conjunction with the Lambertian-equivalent reflectivity model to provide an effective radiative cloud fraction and scattering pressure in the presence of broken or thin cloud. The derived cloud pressures will enable accurate retrievals of trace gas mixing ratios, including ozone, in the troposphere within and above clouds. We describe details of the algorithm that will be used for the first release of these products. We compare our scattering cloud pressures with cloud-top pressures and other cloud properties from the Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument. OMI and MODIS are part of the so-called A-train satellites flying in formation within 30 min of each other. Differences between OMI and MODIS are expected because the MODIS observations in the thermal infrared are more sensitive to the cloud top whereas the backscattered photons in the ultraviolet can penetrate deeper into clouds. Radiative transfer calculations are consistent with the observed differences. The OMI cloud pressures are shown to be correlated with the cirrus reflectance. This relationship indicates that OMI can probe through thin or moderately thick cirrus to lower lying water clouds. [ABSTRACT FROM AUTHOR]

Satellite observations of polar stratospheric clouds (PSCs) in the mid-infrared by high resolution limb emission spectrometers like the Michelson Interferometer for Passive Atmospheric Sounding have been simulated. For particles with radius >1 μm the scattered tropospheric radiance accounts for a significant part of the continuum signal and leads to absorption line features overlaid over the stratospheric emission spectrum. The scattered radiance shows a strong dependence on particle size up to about 7 μm radius with a maximum around 3–4 μm. The contribution of scattered radiation depends heavily on tropospheric cloud coverage and earth surface temperature. Distinction of PSCs of different composition is possible for small particles (<1 μm) due to differences in the imaginary part of the refractive index. For particles with radii between 1 and 5 μm the simulated spectra for various PSC compositions differ due to different real parts of the refractive index. For larger particles no distinction is possible any more. Solar radiance scattered by PSCs is important for wavenumbers larger than about 1700 cm−1. For a forward scattering geometry with 30° between the position of the sun and the limb viewing direction solar contribution exceeds the terrestrial scattered radiation by about a factor of 10. [Copyright &y& Elsevier]

We compared in situ and laboratory velocity and attenuation values measured in seafloor sediments from the shallow water delta of the Eel River, California. This region receives a substantial volume of fluvial sediment that is discharged annually onto the shelf. Additionally, a high input of fluvial sediments during storms generates flood deposits that are characterized by thin beds of variable grain-sizes between the 40- and 90-m isobaths. The main objectives of this study were (1) to investigate signatures of seafloor processes on geoacoustic and physical properties, and (2) to evaluate differences between geoacoustic parameters measured in situ at acoustic (7.5 kHz) and in the laboratory at ultrasonic (400 kHz) frequencies. The in situ acoustic measurements were conducted between 60 and 100 m of water depth. Wet-bulk density and porosity profiles were obtained to 1.15 m below seafloor (m bsf) using gravity cores of the mostly cohesive fine-grained sediments across- and along-shelf. Physical and geoacoustic properties from six selected sites obtained on the Eel margin revealed the following. (1) Sound speed and wet-bulk density strongly correlated in most cases. (2) Sediment compaction with depth generally led to increased sound speed and density, while porosity and in situ attenuation values decreased. (3) Sound speed was higher in coarser- than in finer-grained sediments, on a maximum average by 80 m s−1. (4) In coarse-grained sediments sound speed was higher in the laboratory (1560 m s−1) than in situ (1520 m s−1). In contrast, average ultrasonic and in situ sound speed in fine-grained sediments showed only little differences (both approximately 1480 m s−1). (5) Greater attenuation was commonly measured in the laboratory (0.4 and 0.8 dB m−1 kHz−1) than in situ (0.02 and 0.65 dB m−1 kHz−1), and remained almost constant below 0.4 m bsf. We attributed discrepancies between laboratory ultrasonic and in situ acoustic measurements to a frequency dependence of velocity and attenuation. In addition, laboratory attenuation was most likely enhanced due to scattering of sound waves at heterogeneities that were on the scale of ultrasonic wavelengths. In contrast, high in situ attenuation values were linked to stratigraphic scattering at thin-bed layers that form along with flood deposits. [Copyright &y& Elsevier]