OPAC-4, an international workshop on occultations for probing atmosphere and climate, took place September 6-10, 2010, in Graz, Austria. OPAC-4 followed the objectives of previous workshops OPAC-3, OPAC-2 and OPAC-1 on the application of atmospheric remote sensing by occultation methods and/or the use of occultation data in atmospheric physics, chemistry, and meteorology. 

OPAC-4’s special focus was on climate applications. More than 100 participants from 19 countries took part in lively scientific discourse on mutual leaing and support, and initiatives for co-operation. The workshop participants from the NARL’s National Space Organization (NSPO) reported on FORMOSAT-3’s current mission performance and FORMOSAT-7’s mission planning. The others unanimously acknowledged FORMOSAT-3’s contribution to the global weather community and expressed their expectation of FORMOSAT-7’s radio occultation (RO) constellation mission. Immediately following OPAC-4, the first workshop of the International Radio Occultation Working Group (IROWG) was conducted in the same venue. 

The IROWG was established as a permanent working group of the Coordination Group for Meteorological Satellites (CGMS) in 2009 to further exploit RO data, and is co-sponsored by CGMS and the World Meteorological Organization (WMO). The IROWG, serving as a part of WMO’s implementation plan for the evolution of the global observing system, is to foster the development of better RO measurements, and impROVement of their utilization; the impROVement of scientific understanding; and the development of international partnerships. The Taiwan participants at OPAC-4 were invited to participate in the first IROWG workshop to share their experiences and views on possible future activities.