We report on a Chandra observation of the Crab Nebula that gives the first clear view of the faint boundary of the Crab's X-ray-emitting Pulsar Wind Neb-ula, or PWN. There is structure in all directions. Fingers, loops, bays, and the South Pulsar Jet all indicate that either filamentary material or the magnetic field are controlling the relativistic electrons. In general, spectra soften as dist...

GPS/MET observations of the tropical atmosphere of the southern hemisphere (5S to 25S) during February 1997 are analysed, when a high amount of convective tropospheric water vapor is at these latitudes. Enhanced gravity wave activity of the lower stratosphere at h=22-28 km is associated to areas of increased tropospheric water vapor pressure at h=4-6 km, regarded as a measure of tropical convec...

ACE is a Canadian satellite mission that will measure and help to understand the chemical and dynamical processes that control the distribution of ozone in the stratosphere. The ACE instruments are a Fourier transform infrared spectrometer, a UV/visible/near IR spectrograph and a two channel solar imager, all working in solar occultation mode.

GPS radio occultation (RO) measurements are a potentially important new source of profile information that can be used in numerical weather prediction (NWP). This paper outlines the options for assimilating the RO measurements into an operational NWP system. The importance of realistic estimates for the observation error estimates is discussed.

Ozone and nitrogen dioxide profiles from the FinROSE chemistry transport model (FinROSE-ctm) are compared with observations from the GOMOS stellar occultation instrument on board the Envisat satellite. Data from 2004 is shown. The focus in the comparison is on polar night middle atmosphere. Also vortex averages are shown.

To reduce the sampling rate in global navigation satellite system (GNSS)-radio occultation receivers, it is essential to establish a suitable estimation of Doppler frequency from the received signal in the satellite onboard receiver. This receiver is usually located on low earth orbit satellite and receives GNSS satellites signal in the occultation situation. The occurred Doppler on the signal ...

The navigation by the stellar refraction is important for a LEO (Low-Earth-Orbit) satellite, especially in GNSS (Global Navigation Satellite System)-denied environment, since it totally autonomous. However, biggest barrier to accurate lies stratospheric density. Therefore, retrieval of density star occultation proposed this paper acquire globally with high accuracy. Compared GPS Positioning Sys...