Florida\u27s Art Consignment Statute: A Trap For The Unwary Artist?

On October 1, 1986, Section 686.501-506 Florida Statutes, became effective, making Florida one of the twenty-six states with an Art Consignment statute

Tomographic Imaging of Traveling Ionospheric Disturbances Using GNSS and Geostationary Satellite Observations

Abstract Traveling ionospheric disturbances (TIDs) are the manifestations of atmospheric gravity waves in the ionosphere. These disturbances have practical importance because they affect satellite navigation technologies such as Global Navigational Satellite System (GNSS), causing degradation in precise positioning applications. They also have scientific significance as their generation mechanisms and propagation are not fully understood. While there are specific instruments that can measure TIDs in certain locations, there is a need for wide-area observations across extended geographical regions to continuously monitor their onset and spatial and temporal characteristics. This paper evaluates the use of observations from ground-based geodetic GNSS receivers to image TIDs using ionospheric tomography and data assimilation. Certain GNSS receivers also monitor signals from geostationary (GEO) satellites, which provide a unique perspective on the TID. The advantage of using the GEO data is investigated. A computerized simulation of GNSS observations is used for evaluation of the Multi-Instrument Data Analysis System (MIDAS) with GEO and regular GNSS geometry. The simulated observations are generated by integrating the electron density through a modeled TID-perturbed dynamic ionosphere between actual receiver and satellite positions. The output 3-D electron density image series generated from the synthetic data by the MIDAS ionospheric tomography and data assimilation algorithm are compared with the input model ionosphere. Results show that GEO geometry improves the reconstruction of medium-scale TIDs (MSTIDs) and smaller LSTIDs in cases where the movement of regular GNSS satellites in Medium Earth orbit (MEO) may otherwise introduce distortions to the observations

Rapid and Accurate Measurement of Polarization and Fading of Weak VHF Signals Obliquely Reflected from Sporadic-E Layers

In the E-region of the ionosphere, at heights between 90 and 130 km, thin patches of enhanced ionization occur intermittently. The electron density in these sporadic-E (Es) clouds can sometimes be so high that radio waves with frequencies up to 150 MHz are obliquely reflected. While this phenomenon is well known, the reflection mechanism itself is not well understood. To investigate this question, an experimental system has been developed for accurate polarimetric and fading measurements of 50 MHz radio waves obliquely reflected by mid-latitude Es layers. The overall sensitivity of the system is optimized by reducing environmental electromagnetic noise, giving the ability to observe weak, short-lived 50 MHz Es propagation events. The effect of the ground reflection on observed polarization is analyzed and the induced amplitude and phase biases are compensated for. It is found that accurate measurements are only possible below the pseudo-Brewster angle. To demonstrate the effectiveness of the system, initial empirical results are presented which provide clear evidence of magneto-ionic double refraction

Mitigation of delay and scintillation effects using MIDAS

MIDAS, a 4D tomographic technique is used to map the ionospheric electron density over Europe. The ionospheric maps are then used to calculate the excess delay at the L1 frequency. The excess delay is applied to correct the pseudorange observations and the improvements to the resulting positioning are calculated. The technique is shown to give navigation solutions comparable to those obtained from dual-frequency receivers and the MIDAS approach is more robust against scintillation. The diurnal trend of the ionospheric delay is well compensated for with the correction technique. Improvements in positioning accuracy during selected days are up to 25m

A realistic simulation framework to evaluate ionospheric tomography

Observation of the 3-dimensional (3-D) electron density of the ionosphere is useful to study large-scale physical processes in space weather events. Ionospheric data assimilation and ionospheric tomography are methods that can create an image of the 3-D electron density distribution. While multiple techniques have been developed over the past 30 years, there are relatively few studies that show the accuracy of the algorithms. This paper outlines a novel simulation approach to test the quality of an ionospheric tomographic inversion. The approach uses observations from incoherent scatter radar (ISR) scans and extrapolates them spatially to create a realistic ionospheric representation. A set of total electron content (TEC) measurements can then be simulated using real geometries from satellites and ground receivers. This data set, for which the ‘truth’ ionosphere is known, is used as input for a tomographic inversion algorithm to estimate the spatial distribution of electron density. The reconstructed ionospheric maps are compared with the truth ionosphere to calculate the difference between the images and the truth. To demonstrate the effectiveness of this simulation framework, an inversion algorithm called MIDAS (Multi-Instrument Data Analysis Software) is evaluated for three geographic regions with differing receiver networks. The results show the importance of the distribution and density of GPS receivers and the use of a realistic prior conditioning of the vertical electron density profile. This paper demonstrates that when these requirements are met, MIDAS can reliably estimate the ionospheric electron density. When the region under study is well covered by GPS receivers, as in mainland Europe or North America, the errors in vertical total electron content (vTEC) are smaller than 1 TECu (2–4%). In regions with fewer and more sparsely distributed receivers, the errors can be as high as 20–40%. This is caused by poor data coverage and poor spatial resolution of the reconstruction, which has an important effect on the calibration process of the algorithm.</p