Introducing two spatial reference frames for regions of

ABSTRACT: The current realization of the North American Datum of 1983 (NAD 83) is defined in terms of a Helmert transformation from the International Terrestrial Reference Frame of 2000 (ITRF00). The parameters of this transformation were chosen, in part, so that horizontal NAD 83 velocities would be zero on average for points interior to the North American tectonic plate. Unfortunately, islands located in the Pacific Ocean move horizontally by as much as several centimeters per year relative to the North American plate. To address this motion, this document introduces two new spatial reference frames in terms of transformations from ITRF00, one frame for regions located on the Pacific tectonic plate (Hawaiia

GPS Solut DOI 10.1007/s10291-012-0255-y ORIGINAL ARTICLE

the National Oceanic and Atmospheric Administration, recently released version 3.1 of the Horizontal Time-Dependent Positioning (HTDP) utility for transforming coordinates across time and between spatial reference frames. HTDP 3.1 introduces improved crustal velocity models for both the contiguous United States and Alaska. The new HTDP version also introduces a model for estimating displacements associated with the magnitude 7.2 El Mayor–Cucapah earthquake of April 4, 2010. In addition, HTDP 3.1 enables its users to transform coordinates between the newly adopted International Terrestrial Reference Frame of 2008 (ITRF2008) and IGS08 reference frames and other popular reference frames, including current realizations of NAD 83 and WGS84. A more convenient format to enter a list of coordinates to be transformed has been added. Users can now also enter dates in the decimal year format as well as the month-day-year format. The new HTDP utility, explanatory material and instructions are available a