The Halogen Occultation Experiment (HALOE) is one of 10 instruments aboard the Upper Research Satellite (UARS). The HALOE instrument was built by an instrument team based at NASA Langley and launched on the UARS on 12th September 1991. Data collection began on 11th October 1991 until 21st November 2005. The Principal Investigator (PI) is Dr James M. Russell III.

The HALOE experiment uses solar occultation to measure vertical profiles of ozone (O3), hydrogen chloride (HCl), Hydrogen Fluoride (HF), methane (CH4), water vapour (H2O), nitric oxide (NO), nitrogen dioxide (NO2), aerosol extinction, and temperature versus pressure with an instantaneous vertical field of view of 1.6 km at the Earth limb.

The instrument achieves near-global coverage with measurements sweeping between high latitudes in one hemisphere and high latitudes in the other over a period of between 2 and 6 weeks. The latitude range covered by the instrument varies over the course of the year between 80°S and 80°N. The maximum northerly and southerly latitudes occur in spring and autumn in the few weeks either side of the equinoxes. The range of altitude of the measurements depends on the channel being used, but measurements cover the stratosphere and lower mesosphere and, in the case of the nitric oxide channel, extend into the lower thermosphere.

HALOE studies the dynamics of polar and other atmospheric regions using the tracers, HF, CH4 and H2O. Studying the trends in HCl and HF will help distinguish the relative importance of anthropogenic versus natural chlorine sources and analyse in detail the development and recovery of the Antarctic ozone hole. Additional studies are intended to identify and assess stratosphere-troposphere exchange.

The BADC holds HALOE data at level 2 (uninterpolated profiles at measurement locations), version 19 for the period 11th Ocotber 1991 to 21st November 2005.

The BADC also holds the HALOE level 3A version 19 data spanning the time period from 11th October 1991 through 21st December 2000. HALOE L3 data is public. Updates through to September 24, 2001 are available directly from GSFC NASA.

The HALOE level 3A data are vertical profiles of methane (CH4), hydrogen chloride (HCl), hydrogen fluoride (HF), nitric oxide (NO), nitrogen dioxide (NO2), water vapor (H2O), ozone (O3), temperature (TEMP), and aerosol extinction (AEXTCH4, AEXTHCL, AEXTHF and AEXTNO), interpolated onto a standard set of vertical levels evenly spaced in pressure, and onto standard times (level 3AT) and standard latitudes (level 3AL). The vertical scan range is from about 10 to 65 km, and the vertical resolution is approximately 2.5 km between pressure levels.