Sea Level Determination in the Spanish Coast Using GNSS-R

GNSS reflectometry (GNSS-R) a technique for the study of variations in the height of sea level and inland waters, and for the study of soil moisture, based on the comparison of the direct and reflected noise signal. The main advantage of this method is that allows the connection between sea level measurements and the global reference frame. The purpose of this contribution is to present the GNSS-R analysis service at the Geodesy department of the National Geographic Institute of Spain and to compare the sea level time series determined by means of GNSS-R with tide gauge measurements. Two different GNSS-R methods using multi-constellation and multi-frequency data are compared: Lomb-Scargle Periodogram and Inverse Modelling. This analysis is performed for 3 GNSS antennas collocated to tide gauges along the Spanish coast. Eventually, advantages and disadvantages of this method are discussed.

PHOTOGRAMMETRIC SURVEY WITH FISHEYE LENS FOR THE CHARACTERIZATION OF THE LA SASSA CAVE

<p><strong>Abstract.</strong> The survey of ancient cave can generally be performed by traditional topographic methods that allow also its georeferencing in a global reference frame; some difficulties may arise when there are narrow tunnels that do not consent the use of a total station or a terrestrial laser scanner. In such cases a visual-based approach can be used to produce, both the followed path and the 3D model of the hypogeal environment. A prompt photogrammetric survey has been used to reconstruct the morphology of the La Sassa Cave, situated in the municipality of Sonnino (Latina), in the lower Lazio region. In this cave, a very large quantity of Pleistocene animal bones was found, together with several fragments of Copper Age human bones and Bronze Age impasto potsherds.</p><p> The survey was carried out using a DSLR full frame camera Nikon D800E with a Nikkor 16<span class="thinspace"></span>mm fisheye lens pre-calibrated. During the acquisition, several targets were measured in order to contain the deformations model. The photogrammetric model has been georeferenced using 3 GCPs positioned outside the cave entrance where a double frequency GNSS receiver has acquired data in static session mode.</p>

Ray Effect Mitigation Through Reference Frame Rotation

The discrete ordinates method is a popular and versatile technique for solving the radiative transport equation, a major drawback of which is the presence of ray effects. Mitigation of ray effects can yield significantly more accurate results and enhanced numerical stability for combined mode codes. When ray effects are present, the solution is seen to be highly dependent upon the relative orientation of the geometry and the global reference frame. This is an undesirable property. A novel ray effect mitigation technique of averaging the computed solution for various reference frame orientations is proposed.

Enabling high-accuracy, position monitoring of Sable Island through the Nova Scotia Coordinate Referencing System

Since 1968, the Province of Nova Scotia has carried out a mandate of providing coordinate referencing infrastructure for its citizens. The current infrastructure is known as the Nova Scotia Coordinate Referencing System (NSCRS) and allows property boundaries, engineering works, and natural features to be spatially related within the Province, including Sable Island. Traditionally, thousands of survey monuments across the Province provided access to the coordinate referencing system for surveying and engineering work. Of the original 23,000 monuments installed in the 1970s and 1980s, many have been destroyed by natural occurrences or human activities. In the case of Sable Island, most have been enveloped by sand or the sea. In 2013, the Province began implementing a modernized strategy for delivering coordinate referencing services to its citizens using permanent GPS stations. This technology was installed at Main Station on Sable Island in June of 2014. This GPS infrastructure has already had a positive impact by:a)Allowing, for the first time, the three dimensional position of Sable Island (specifically Main Station) to be monitored with millimeter level accuracy b)Enabling Light Detection and Ranging (LiDAR) and aerial photography surveys to be consistently referenced within a global reference frame; andc)Providing quick and accurate positioning of natural features around the island with millimeter level accuracy and consequently enabling long term, position trends of these features (e.g., Bald Dune) to be determined.Each of these topics is discussed and a history of the NSCRS on Sable Island is presented.

Tolerance-Maps for Line-Profiles Formed by Intersecting Kinematically Transformed Primitive Tolerance-Map Elements

For the purposes of automating the assignment of tolerances during design, a math model, called the Tolerance-Map (T-Map), has been produced for most of the tolerance classes that are used by designers. Each T-Map is a hypothetical point-space that represents the geometric variations of a feature in its tolerance-zone. Of the six tolerance classes defined in the ASME/ANSI/ISO Standards, profile tolerances have received the least attention for representation in computer models. The objective of this paper is to provide a comprehensive treatment of T-Map construction for any line-profile by using primitive T-Map elements and their Boolean intersection. The method requires (a) decomposing a profile into segments, each of constant curvature; (b) creating a solid-model T-Map primitive for each in a common global reference frame; and (c) combining these by Boolean intersection to generate the T-Map for a complete line-profile of any shape. Freeform portions of a profile are modeled as a series of closely spaced points and subsequent formation of short circular arc-segments, each formed from the circle that osculates to three adjacent points.