![]() ![]() The geolocation bias at the edge of the scan line before/after correction is 4.6/1.3 km at K-band, 9.4/1.8 km at Ka-band, 4.4/2.4 km at V-band, and 3.2/0.8 km at W-band. The total geolocation error at nadir before/after correction is 3.8/0.8 km at K-band, 5.6/0.8 km at Ka-band, 3.3/0.4 km at V-band, and 1.5/0.1 km at W-band. By using the correction matrix built in this paper, the geolocation error is obviously reduced both at nadir and at the edge of the scan. A mathematical model is then developed to convert the in-track and cross-track geolocation errors to the beam pointing Euler angles defined in the spacecraft coordinate system, which can be further used to construct the correction matrix for on-orbit geolocation process. It is disclosed that for SNPP ATMS, the static error term with scan-angle-dependent feature is a dominant part among all the geolocation error sources. In this paper, a refined coastline inflection point method is used to evaluate the on-orbit geolocation accuracy of SNPP ATMS. In addition, USNO Circular 181 provides greater detail on the handlingįor the quantitative applications of the Suomi National Polar-orbiting Partnership (SNPP) Advanced Technology Microwave Sounder (ATMS), the geolocation accuracy of its sensor data records must be quantified during its on-orbit operation. NOVAS, including its User's Guide (USNO Circular 180), is available from ICRS-compatible data, e.g., the Hipparcos, Tycho-2, UCAC, 2MASS and VCSĬatalogs, the JPL planetary and lunar ephemerides, and IERS Earth Inside and outside the solar system similarly. That does not use spherical trigonometry at any point. NOVAS algorithms are based on a rigorous vector and matrix formulation In addition, new convenience functions have NOVAS also improves the accuracy of its star and planet positionĬalculations by including several small effects not previously (USNO Circular 179ĭescribes these IAU resolutions in detail.) NOVAS now incorporates aĬoherent set of foundational standards for the treatment of astrometricĭata and the modeling of dynamics in the solar system. Systems, time scales, and Earth rotation models. NOVAS Version 3.0 was recently released with extensive revisions to theĬode in response to recent IAU resolutions on astronomical reference parts of The Astronomical Almanac uses NOVAS. Reduction programs, telescope control systems, and simulations. Package is an easy-to-use facility that can be incorporated into data Those for precession, nutation, aberration, parallax, etc. ![]() Single-purpose subroutines for common astrometric algorithms, such as NOVAS also provides access toĪll of the "building blocks” that go into such computations: Planet in a variety of coordinate systems. It can supply, in one or two subroutine orįunction calls, the instantaneous celestial position of any star or Source-code library in Fortran and C that provides common astrometric Vectorial astrometry by c a murray pdf software#The usual vector operations – addition, subtraction, multiplication by a scalar, scalar (dot) product, and vector (cross) product – have simple geometrical interpretations that are independent of the coordinate system.The Naval Observatory Vector Astrometry Software (NOVAS) is a Vectors can be visualized as arrows that exist in space quite independently of any coordinate system. In this section we define classical vectors, unit vectors, matrices and present some important formulae for manipulating them.Ĭlassically, a vector is defined as a physical entity having both magnitude (length) and direction, as opposed to a scalar that only has magnitude. Only vectors in three-dimensional Euclidean space are considered. By way of illustration, some useful transformations are explained in detail, while references to the general literature are provided for other applications. Murray's Vectorial Astrometry (1983), which seem to provide a particularly clear and consistent framework for theoretical work as well as practical calculations. ![]() It broadly uses the notational conventions from C. This chapter provides a brief introduction to the use of vectors and matrices in astrometry. It turns out that this often provides a better insight into the problem, and hence reduces the risk of errors in the derived algorithms, in addition to being advantageous in terms of computational speed and accuracy. Practical calculations using computer software are today mainly carried out with the help of vector and matrix algebra, rather than the trigonometry formulae typically found in older textbooks. In astrometry, vectors are extensively used to describe the geometrical relationships among celestial bodies, for example between the observer and the observed object. ![]()
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