Posts

Why are GNSS Carrier Signals in the L-Band?

The L band, as defined by the IEEE (Institute of Electrical and Electronics Engineers), is the 1 to 2 GHz range of the radio spectrum. The L band consists of two components, Aviation Radio Navigation Service (ARNS) and Radio Navigation Satellite Service (RNSS) and is utilized in many radar, satellite and terrestrial communications applications. The L band has several advantages which marks it suitable for GNSSs. The L band has a low bandwidth due to its low frequency range.

The eclipsing satellite

An eclipse is an event that occurs when an object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. During an eclipse there are three main phases the object can experience. ​These phases include: Umbra (Latin for “shadow”) - The innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body.

Navigating through the sea of GNSS hardware manufacturers

With an exponentially growing GNSS market, it can quickly become overwhelming when trying to decide on the ideal receiver that would meet a client’s specifications. Because of this, I began collecting information on different GNSS receivers with the aim of developing a web utility that would allow the user to enter their specifications and the utility recommend suitable receivers. Over the pass couple months, I’ve been collecting publicly available information on different types of GNSS receivers.

What is time?

Recently, my research has shifted away from GNSS positioning and more towards clocks. I’ve been examining different products for correcting satellite clock errors and different strategies for combining the products. Looking at the variations in the GNSS timing system, a timing system some people would describe as an absolute measure of time, motivated the question, “What is time?”. Time, measured by a clock, may be considered as a two-part device.

Am I a Geodesist?

Motivated by one of UNAVCO’s videos entitled, “Do You Call Yourself A Geodesist?” I began to wonder, am I a Geodesist? Who is a Geodesist? A geodesist measures the Earth’s surface as well as studies the science and shape of the planet and gravitational field. Measurements are taken of the size of Earth on a global and regional scale. By taking these measurements of the Earth, crustal shifts and polar movement can be detected.

Date Conversion Utility

It has been several weeks since I’ve made any substantial posts to the blog. I’ve been working on several projects while trying to maintain a consistent pace with the Ph. D. research. Finally, I have a complete product from one of my projects that I am able to share. Presented, is my first web based application that allows users to transform between different time systems. While the utility lacks novelty as there are other applications online with similar functionality, the focus of developing the web application was an exercise to learn R programming.

Summary of GNSS parameters

Paramters for each of the GNSS table.tableizer-table { border: 1px solid #CCC; font-family: Arial, Helvetica, sans-serif; font-size: 12px; } .tableizer-table td { padding: 4px; margin: 3px; border: 1px solid #ccc; } .tableizer-table th { padding: 4px; margin: 3px; border: 1px solid #ccc; font-weight: bold; } ParameterGPSGLONASSGalileoBeidou First launch22-Feb-7812-Oct-8228-Dec-0513-Apr-07 FOC17-Jul-9518-Jan-9620122013 Servicesmilitarymilitarycommercialauthorized civilcivilopenopen/commercial Number of SV31242727 Orbital planes6333 Inclination55°64.8°56°55° Semi-major Axis [Km]26560255082960127840 Period11h58m11h15m14h05m12h50m Coordinate frameWGS-84PZ-90GTRFCGCS2000 Time systemGPSTUTC (SU)GSTChina UTC CodingCDMAFDMACDMACDMA Frequencies [MHz]L1:1575.42G1:1602E1:1575.42B1-2:1589.74 L2:1227.

PZ-90 terrestrial coordinate system for GLONASS

In fulfillment of the Russian Government Resolution No 1463 of December 28, 2012 “On the Common National Geodetic Coordinate Systems” starting from 3:00 pm on December 31, 2013 the transition to using the terrestrial geocentric coordinate system “Parametry Zemli 1990” (PZ-90.11) in operating the GLObal NAvigation Satellite System (GLONASS) has been implemented. The update to the reference system from PZ-90.02 apparently consists of an origin shift, small rotations of the axes, and a small scale change, all made in an effort to improve the alignment with respect to ITRF.

GNSS sky plots

Sky plots are polar orthogonal plots illustrating the satellite’s path as a function of elevation and azimuth which can be used in GNSS survey planning. Sky plots illustrates the geometry of the satellite constellation which is expressed mathematically as the geometric dilution of precision (GDOP) factor, Presented, is the matlab code used to generate the figure on left using data from the reference station ALGO on DOY 62 2008 at 12:00 GPS Time.

Plotting MATLAB figures for journals

One of the most frustrating tasks I encountered while using MATLAB was to output and store figures that were high resolution and the font size would be legible when copied into double column journals. Copying the figures directly (Edit -> Copy figure) works well but I always preferred to have my scripts run and have the files stored automatically to an assigned folder. The attached code is what I currently used.