High Accuracy Satellite Research Articles

DORIS-DIODE: two-years results of the first European Navigator

The DORIS system was developed to support high accuracy orbit determination and beacon positioning. For the first time, thanks to DIODE, the SPOT-4 satellite orbit is determined in real time on-board with an accuracy of 3–5 meters. Two year DIODE/SPOT-4 monitoring shows that this Navigator has been operational 99.4 % of the time with a few meters accuracy, even through maneuvers. An improved version of DIODE will be loaded on board SPOT-4 next year and will fly, including new upgrades, on board Jason-1, ENVISAT and SPOT-5. Simulations performed using TOPEX/POSEIDON DORIS measurements show that a sub-meter accuracy will be reached with Jason-1.

Comparison and Accuracy Assessment of Semi-Empirical Atmosphere Models through the Orbital Decay of Spherical Satellites

A detailed comparison and assessment of the accuracy of semi-empirical atmospheric density models (JR-71, MSIS-86/90, TD-88) were carried out by analyzing the orbital decay of nine spherical satellites in the 150-1500 km altitude range. The orbital decay data used were distributed over a full solar activity cycle (1987-1999). The drag coefficients which were estimated by fitting the observed semimajor axis evolution with a high accuracy orbit propagator were compared with those computed by theoretical analysis. While MSIS-86/90 proved to be the best model to compute the air density below 400 km, in low solar activity conditions, JR-71 was more accurate at greater altitudes and/or solar fluxes. TD-88, defined below 700 km, was quite accurate (10%) only during periods of moderate solar activity. Between 350 and 800 km, the average accuracy of JR-71 and MSIS-86/90 was generally better than 15% and, sometimes, even better than 10%. However, at 1500 km and during low solar activity conditions, both models underestimated the air density by 60%, while below 350 km, still during low solar activity conditions, they overestimated the air density by 20-25% and 10-20%, respectively.

Space-Based Space Surveillance with the Space-Based Visible

Space surveillance is the activity of keeping a current catalog of information on manufactured, Earth-bound resident space objects. Some necessary functions to perform this task are search and detection, acquisition and tracking, tasking and scheduling, and data reduction and processing. The Midcourse Space Experiment satellite, launched 24April 1996, carries the Space-Based Visible sensor packagedesigned for conducting space surveillance froma spaceplatform.Other contributionsto this issue discuss Space-BasedVisible operations,data reduction, and accuracy. The Space-Based Visible provides high-accuracy angle measurements (right ascension and declination). Based on these data, space-based space surveillance catalog maintenance can be demonstrated. To this end, orbits are calculated based on ground-based data, space-based data, and various combinations of these data. From these results a number of surveillance functions can be demonstrated, for example, compatibility and fusion of space-based and ground-based metric (position) data. When an independent, high-accuracy orbit is available, an assessment of the orbit accuracy is made. In other cases, differences between the orbits are computed. In addition, access to the complete geosynchronous belt and catalog maintenance for geosynchronous satellites will be demonstrated. Effectiveness of space-based space surveillance data is assessed.

ADEOS-II precise orbit determinations with GPS and SLR

In order to meet the scientific mission requirements for high accuracy orbit determination strongly required by future earth observation missions in the early 2000's, NASDA's precise orbit determination system with GPS (Global Positioning System) and SLR (Satellite Laser Ranging) is now being developed at the NASDA/TACC (Tracking and Control Center). This system, which is called GUTS (Global and high accUracy Trajectory determination System), will be used to demonstrate precise orbit determination with ADEOS-II (Advanced Earth Observing Satellite II), set for launch in the year 2000. This paper presents an overview of the GUTS and its experimental and operational plans.

Spot-4 vegetation instrument: Vegetation monitoring on a global scale

Vegetation plays a major role in global climatic change. It is a major contributor to the hydrological cycle and carbon exchanges between the Earth's surface and the atmosphere. A new space-based system dedicated to vegetation would be a boom to climatic and environmental studies. The additional possibilities of evaluating agricultural, pasture and forest production would be major contributions to improved natural resources management and a special benefit to agriculture and the general economy in developing countries. A space mission for monitoring terrestrial vegetation at global and local levels is proposed for inclusion in the Spot-4 payload, scheduled for launch around 1997. The “vegetation” concept is more than just an on-board package; it is a complete system with its own space and ground segments. The vegetation instrument (VI) on-board package is designed as an add-on payload that is quite independent of the host satellite. In addition to the basic imaging instrument, the add-on payload includes a solid-state recorder, an image telemetry subsystem and a computer to manage the work plan. To accommodate future long-term missions and achieve a lifetime in excess of 5 years, no moving parts are included in either the imaging instrument proper or the recorder subsystem. The innovative, large field-of-view (101∘) imaging instrument features telecentric lenses and focal-plane illumination compensation. Despite the large FOV, pixel size varies extremely little across the swath. Overall, the instrument offers an excellent revisit capability at the highest resolution. The inclusion of the VI package alongside Spot-4's prime payload of two HRVIR (high resolution visible and i.r.) imaging instruments will open the way to studies requiring both high accuracy satellite imagery and short revisit intervals. The combination of HRVIR and VI imagery will pave the way to powerful new multi-scale interpretation models, particularly as the instruments will share the same spectral bands, have a common reference frame and be synchronized in time.

A demonstration of sub meter GPS orbit determination and high precision user positioning

High-accuracy orbits have been determined for satellites of the Global Positioning System (GPS), with submeter orbit accuracy demonstrated for two well-tracked satellites. Baselines of up to 2000 km in North America determined with the GPS orbits shows daily repeatability of 0.3-2 parts in 10/sup 8/ and agree with very long baseline interferometry (VLBI) solutions at the level of 1.5 parts in 10/sup 8/. Tests used to assess orbit accuracy include orbit repeatability from independent data sets, orbit prediction, ground baseline determination, and formal errors. One satellite tracked for eight hours each day shows RMS errors below 1 m even when predicted more than three days outside of a 1-week data arc. These results demonstrate the powerful relative positioning capability available from differential GPS tracking. Baselines have also been estimated between Florida and sites in the Caribbean region over 1000 km away, with daily repeatability of 1-4 parts in 10/sup 8/. The best orbit estimation strategies included data arcs of 1-2 weeks, process noise models for tropospheric fluctuations, combined processing of GPS carrier phase and pseudorange data, and estimation of GPS solar pressure coefficients.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Atmospheric tidal perturbation of artificial satellite orbits

Abstract We derive an analytical expression for the perturbation due to atmospheric tide and estimate its order of magnitude. For LAGEOS, over a 5-day arc, the perturbation generates an along-track error of about 20 cm. The perturbation due to atmospheric tide is on the order of 5(−11), or 2.6% of that due to the solid tide; hence it should be included in high accuracy orbit determination.

Surveying and Geodesy in Australia with GPS

Abstract The Global Positioning System (GPS) is an all weather, high accuracy satellite positioning system that will drastically change the way in which many surveying tasks are presently carried out. One purpose of this article is to familiarise the surveyor with the GPS technology. The possible impact of the technique on the entire spectrum of surveying activities is also assessed. For everyday surveying, GPS is unlikely to displace EDM and the theodolite, but it will be competitive if present instrument costs are reduced. In geodesy GPS will replace all techniques currently used for determining positions of points separated by more than a few tens of kilometres. Its immediate use for geodynamics is most advantageous over distances ranging from 30 to 300 km. In Australia, the successful introduction of GPS for geodesy and high precision surveying applications hinges on the establishment of an orbit determination facility. This facility would also benefit the general surveying community.

Satellite Laser Altimeter for Measurement of Ice Sheet Topography

We describe the design and expected performance of a spaceborne laser altimeter based on a nadir-oriented laser transmitter, a 0.5-m-diam receiver telescope, and a high-accuracy satellite attitude measurement system. This instrument is designed for high-resolution mapping of polar ice sheet topography where conventional radar altimeters have difficulty. This instrument could also provide useful data on cloud-top heights and the ocean surface.

Radiometric Calibrations for the Earth Radiation Budget Experiment

The earth radiation budget (ERB) experiment is scheduled to be flown aboard the NIMBUS F satellite that is to be launched in mid-1974. This experiment includes channels, to measure solar radiation, earth-reflected radiation (albedo), and earth-emitted long-wave radiation. The calibration techniques and the standards employed are included in the topics of this paper. Problems associated with achieving the desired levels of confidence for a multifaceted, high accuracy satellite experiment are discussed and some results of preliminary calibrations are presented.