Amir Allahvirdi-Zadeh

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• PhD
• Lecturer at Curtin University

This paper investigates the potential of signals of opportunity for positioning using broadband low Earth orbit constellations. We developed analytical absolute and differential models based on Doppler-shift observations from multi-constellation satellite bursts across various frequency ranges. Owing to the unavailability of multi-constellation bro...

CubeSats hold promise for various applications, but their viability in demanding missions such as future low Earth orbiting position, navigation, and timing (LEO-PNT) systems hinges on higher orbital accuracy and reliable attitude information. To address these challenges, we present an array-aided combined precise orbit and attitude determination m...

Low earth orbit (LEO) constellations offer possible significant augmentation to the Global Navigation Satellite Systems (GNSS) for positioning, navigation, and timing (PNT) applications. This study explores a new application of forthcoming LEO-PNT constellations; the utilization of signals from higher LEO satellites for precise orbit determination...

Precise orbit determination (POD) is the procedure for determining the orbit of a satellite with high accuracy. Compared with global navigation satellite systems (GNSS), the low Earth orbit (LEO) satellites have some different features in space, mainly due to perturbations caused by dynamic forces related to their altitudes. Methods for POD of LEO...

For real-time precise orbit determination (POD) of low earth orbit (LEO) satellites, high-accuracy global navigation satellite system (GNSS) orbit and clock products are necessary in real time. Recently, the Japanese multi-GNSS advanced demonstration of orbit and clock analysis precise point positioning (PPP) service and the new generation of the A...

To achieve high-accuracy positioning and timing in real time using Low Earth Orbit (LEO) navigation signals, the precision of the orbital products is of high necessity. Reduced-dynamic LEO satellite Precise Orbit determination (POD) can nowadays provide near-real-time orbits with an accuracy of centimeters, and real-time users can rely on broadcast...

Real-time integrity monitoring (IM) is essential for autonomous vehicle positioning, requiring high availability and manageable computational load. This research proposes using precise point positioning real-time kinematic (PPP-RTK) as the positioning method, combined with an improved classification adaptive Kalman filter (CAKF) for processing. PPP...

Underwater photogrammetry has gained popularity for creating three-dimensional (3D) maps and ortho-images of marine environments as compared to traditional echosounder surveys, they can be more cost-effective at creating high-resolution 3D models, and orthoimages are usually more informative than acoustic backscatter maps. This paper builds on prev...

Two approaches are discussed for the estimation and prediction of the orbits of low earth orbit (LEO) satellites that can be used for navigation. The first approach relays on using a ground monitoring network of stations. The procedures to generate the LEO orbital products in this approach are proposed at two accuracy levels to facilitate different...

Absolute or relative precise orbit determination (POD) is an essential prerequisite for many low earth orbit (LEO) missions. The POD of LEO satellites typically relays on processing the onboard global navigation satellite system (GNSS) measurements. The absolute POD is usually based on an ionosphere-free (IF) combination, and currently, integer amb...

Low Earth orbit (LEO) satellites are widely used in space missions such as satellite gravimetry, radio occultation, Earth monitoring, and in formation flying. Precise orbit determination (POD), in either absolute or relative modes, is an essential prerequisite for these missions. The onboard collected signals of the global navigation satellite syst...

CubeSats are faced with some limitations, mainly due to the limited onboard power and the quality of the onboard sensors. These limitations significantly reduce CubeSats' applicability in space missions requiring high orbital accuracy. This thesis first investigates the limitations in the precise orbit determination of CubeSats and next develops al...

The attitude information of a CubeSat is essential to keeping the satellite in its favourable orientations in the mission and sensor positioning using precise orbit determination. The attitude of CubeSats can be determined using sun sensors, magnetometers, and star trackers. However, these sensors have some issues, including unavailability in shado...

Signals from the emerging Low Earth Orbit (LEO) satellites from mega-constellations that broadcast internet, such as Starlink (Space X), OneWeb, Iridium etc., also known as "signals of opportunity" (SOP), can potentially aid positioning. These LEO satellites are approximately 20 times closer to Earth compared to the GNSS medium-earth orbit (MEO) sa...

Presented at FIG Congress 2022, 11-15 September 2022, Warsaw, Poland

This is the presentation of Milestone 1 (Candidacy) at Curtin University

This is the final Presentation of my PhD project.

CubeSats can be used for many space missions and Earth science applications if their orbits can be determined precisely. The Precise Orbit Determination (POD) methods are well developed for large LEO satellites during the last two decades. However, CubeSats are built from Commercial Off-The-Shelf (COTS) components and have their own characteristics...

The use of CubeSats is expanding in space and earth science applications due to the low costs of building and the possibility of launching them in a large low-earth orbits (LEO) constellation. Such constellation can serve as an augmentation system for positioning, navigation and timing. However, real-time precise orbit determination (POD) is still...

The first release of the toolbox is available on my GitHub: https://github.com/AmirAllahvirdi/shadow Feel free to use it! For more information read the release note.

Global Navigation Satellite Systems’ radio occultation (GNSS-RO) provides the upper troposphere-lower stratosphere (UTLS) vertical atmospheric profiles that are complementing radiosonde and reanalysis data. Such data are employed in the numerical weather prediction (NWP) models used to forecast global weather as well as in climate change studies. T...

CubeSats as small Low Earth Orbiting (LEO) satellites are equipped with space-based receiver and antenna capable of tracking Global Navigation Satellite Systems (GNSS). These GNSS signals provide the possibility of precise orbit determinations (POD) of the CubeSats which is essential for different earth and space science applications. Examples of t...

This poster has been presented at the Scientific Assembly of the International Association of Geodesy (IAG2021) conference has been held from Jun 28 to Jul 02, 2021, in Beijing, China. It is about using a new weighting model based on SIgnal-to-Noise Ratio (SNR) for the precise orbit determination of CubeSats. The related peer-review paper will be...

What if we use software-defined radio (SDR) instead of/beside the GNSS receivers onboard the CubeSats?

Making use of dual-frequency (DF) global navigation satellite system (GNSS) observations and good dynamic models, the precise orbit determination (POD) for the satellites on low earth orbits has been intensively investigated in the last decades and has achieved an accuracy of centimeters. With the rapidly increasing number of the CubeSat missions i...

Precise Positioning by smartphones is in the early steps. In this presentation, an overview of this novel subject is discussed and possible future works are introduced.

It is about IGS and its structure. I introduce data and products that are available through IGS data centers to the SAMT users. SAMT is a Real-Time Kinematic (RTK) service in Tehran. (Text in Persian)

GPS draconitic signal (351.6 ± 0.2 days) and its higher harmonics are observed at almost all IGS products such as position time series of IGS permanent stations. Orbital error and multipath are known as two possible sources of these signals. The effect of Earth shadow crossing of GPS satellites is another suspect for this signal. Up to now there is...

"Extraction atmospheric parameters of GPS data" is the title of a workshop I held for the cloud seeding staff and graduate students of the Physics department of Yazd University. It was about how to extract atmospheric parameters from GPS data and services and analyze them to calculate the Predicted Water Vapor (PWV).

Analysis of Radio Occultation Data with Rom SAF V8 and MATLAB and create related files. It was a part of research with the faculty members of the Physics department of Yazd university.

The Shadow toolbox is a Matlab toolbox that is written for detecting satellites in the shadow of the Earth. The input is a RINEX observation file and the output is the new and refined RINEX observation file excluding the observations of the GNSS satellites at the shadow of the Earth. http://dx.doi.org/10.6084/m9.figshare.19085546.v1

Spectral analysis of time series is an important issue in Geodesy. The main purposes of this analysis are detecting periodic behavior and the sources of these behaviors. Periodic signals and their harmonics are causes of reduced accuracy in time series analysis. Therefore these signals should be detected and removed from the results. One of these P...

"Collecting and Processing a GNSS network using GNSS receivers" was a workshop that I held at the University of Ardestan. I taught the undergrad students how to collect the required GNSS observations for network processing using GNSS receivers and then how to process them to reach the highest coordinates useful for surveying purposes.

This code gets the total electron content (TEC) files and plots the variation of the TEC map in Matlab.

This code get the precise ephemeris and interpolate the satellite position to the requested time.

I introduced the International GNSS Service in the internal students' seminar at the University of Isfahan: The International GNSS Service (IGS) has ensured open access, high-quality GNSS data products since 1994. These products enable access to the definitive global reference frame for scientific, educational, and commercial applications – a tre...

I introduced the International Earth Rotation and Reference Systems Service (IERS) at the University of Isfahan: The IERS was established in 1987 by the International Astronomical Union and the International Union of Geodesy and Geophysics. According to the Terms of Reference, the IERS accomplishes its mission through the following components: Tec...

I introduced the International Laser Ranging Service (ILRS), its data and products in the internal student's seminar at the University of Isfahan: Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) use short-pulse lasers and state-of-the-art optical receivers and timing electronics to measure the two-way time of flight (and hence distance)...

I introduced the international Doris Service in the internal seminars of the University of Isfahan. The Doris system is a french civil precise orbit determination and positioning system. It is based on the principle of the Doppler effect with a transmitting terrestrial beacons network and onboard instruments on the satellite's payload (antenna, ra...

In this project, I will demonstrate the process of analyzing GPS time-series data. I have used 10 years of continuous GPS measurements of four stations (ALGO, GRAZ, KOSG, and ONSA) and three different combinations of the noise component of GPS coordinate time-series, i.e., White noise, Flicker noise, and random walk noise. I use Least Squares Varia...

The principles of Quality Control and the instructions for using TEQC are discussed.