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Naval Meteorology and Oceanography Command U.S. Naval Observatory
Monday February 20, 2017

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USNO Analysis of IVS-CRF Experiments

The IVS schedules regular celestial reference frame (CRF) observations for the specific purpose of improvement of the ICRF. In recent years, these CRF sessions have concentrated primarily on observations of sources in the southern hemisphere. Of order 16 CRF sessions per year are scheduled and observed. Geodetic and/or astronomical telescopes located in Australia, South America, South Africa, Japan, Italy and Hawaii are used. IVS-CRF and IVS-CRDS observations concentrate primarily on 1) obtaining more accurate positions of existing ICRF sources (notably Defining Sources) by adding additional observations and 2) obtaining source position stability information from time series at useful time resolution.

  • Status - 2006 February 17 (based on USNO crf2006a)

    Sources observed in CRF experiments were orignally selected from the pool of southern hemisphere ICRF sources. The primary selection criteria was that they were not actively being observed in any other observing program. From the original list, a total of approximately 100 regularly detectable sources remain. An additional 24 sources that are new since ICRF-Ext.2 have been added bringing the total number of sources being actively observed to 124.

    Figure 1: The distribution of all 124 sources an Aitoff equal area projection of the celestial sphere (PS, JPG).

    Figure 2: The percentage increase in the number of delay observations since ICRF-Ext.1 for all 124 sources (PS, JPG). ICRF Defining sources are marked with a red circle (all 212 sources are shown).

    Figure 3: The number of epochs per source (i.e. positions measurments) observed since 2002 January for all 124 sources shown as a histogram (PS, JPG) and as a function of source declination (PS, JPG).

    Figure 4: The weighted rms position variation versus reduced Chi^2 for all 124 sources taken from the USNO crf2006a position time series for all epochs (PS, JPG).

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