New Zealand and Antarctic first-order geomagnetic repeat observations 1990-1992

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McKnight, J.D. 1993 New Zealand and Antarctic first-order geomagnetic repeat observations 1990-1992. Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 93/49 62 p.

Abstract: A network of repeat stations is maintained throughout the New Zealand region and in Antarctica at which periodic observations of the geomagnetic field are made for the purpose of monitoring its secular variation. In 1990 a first- order observing process was adopted and in the period up to the end of 1992 most of the stations in the network were reoccupied, some of them twice. This report describes the stations and the reoccupations and presents the results. A first-order reoccupation involves running a portable digital three-component fluxgate variometer on a station for a period spanning at least two nights and making absolute observations during the intervening day. The absolute observations are used subsequently to calibrate the variometer. An ''undisturbed'' field value for the station is determined from the calibrated variometer record and with reference to longer-term records from the nearest observatory. The difference between ''undisturbed'' field values determined on separate reoccupations of a single station is a measure of the secular variation at that station. The results of the 32 repeat station reoccupations made between December 1990 and December 1992 are given. The results include details of the absolute observations made, the mean hourly values of the field recorded by the variometer and the ''undisturbed'' or adopted field values for each reoccupation. Information about the repeat stations, the reference marks used and further work required at the stations is also given. (auth)