Spectroscopy Introduction



Spectral analysis of RHESSI data is currently a two step process. The spectroscopy object first produces a count-rate spectrum with corrections for all known instrumental effects. It is computed in the RHESSI spectroscopy object and can also be generated in the GUI. This count-rate spectrum is then input to the spectroscopy package - either OSPEX or SPEX.  This converts the count-rate spectrum into the spectrum of the incident photons using various selectable spectral forms such as thermal and power law.

SPEX, or Spectral Analysis Executive, was written by Richard Schwartz in the early 1990's. OSPEX, or Object Spectral Analysis Executive, written by Kim Tolbert in 2004 is the next generation of SPEX.   SPEX will continue to function as is, but will not be updated.  SPEX was developed originally to analyze spectral information from the Hard X-ray Burst Spectrometer on the Solar Maximum Mission (SMM) and from the BATSE instrument on CGRO.  It was expanded to include RHESSI in 2002.  OSPEX is evolving;  it will be enhanced over time and expanded to include more instruments for analysis.  Currently OSPEX includes RHESSI spectrum and image cube input, as well as SMART-1 XSM, SOXS, MESSENGER, and FERMI GBM.

OSPEX and SPEX provide a uniform interface suitable for the spectral analysis of data from a number of solar (or other) instruments in the X-ray and gamma-ray energy ranges. These packages are suitable for any data stream that can be placed in the form of response vs. interval, where the response is usually a counting rate (spectrum) and the interval is normally an accumulation over time.

Together with an algorithm to relate a model input spectrum to the observed response, generally a response matrix, the data set is amenable to analysis with this package. The instrument response matrix details the probability of a photon of any energy producing a pulse in the detector of a given amplitude. The response functions for the RHESSI detectors have been developed by David Smith and are available on line for use with SPEX or OSPEX.










Responsible NASA Official:
Brian Dennis
Web Design:
Merrick Berg

Solar Physics Laboratory, Goddard Space Flight Center

Space Science Laboratory, University of California Berkeley
Responsible Berkeley Official:
Hugh Hudson
Systems Admin:
Jon Loran

This page last updated: June 27, 2011