Chapter 5. HIFI Calibration

Table of Contents

5.1. Introduction:
5.2. The Intensity Calibration of HIFI
5.2.1. Context
5.3. The HIFI Calibration Scheme
5.3.1. Internal Load Calibrations
5.3.2. OFF calibration
5.3.3. Differencing observations:
5.3.4. Non-linearity:
5.3.5. Blank-sky contribution:
5.3.6. Conversion between Antenna Temperature and Janskys:
5.4. The Frequency Calibration of HIFI:
5.4.1. Context:
5.4.2. Frequency accuracy:
5.4.3. Determination of Frequency Calibration:
5.4.4. Frequency resolution:
5.4.5. Frequency and Velocity Verifications
5.4.6. Spurious Responses in HIFI
5.5. The Spatial Response Calibration of HIFI:
5.5.1. Context:
5.5.2. Beam Characteristics
5.5.3. Chopper Calibration
5.6. Mixer Side-band Ratio
5.6.1. IF Spectrum Repeatability (Sideband Line Ratios)
5.6.2. Summary Sideband Ratio Information
5.6.3. Intrinsic sideband ratio IF dependence
5.7. Summary: overall calibration of HIFI and error budget:
5.7.1. Strategy summary:
5.7.2. Error budget

5.1. Introduction:

This chapter gives a general view of the calibration concepts chosen for the HIFI instrument. This chapter is intended to provide an overview of how HIFI is calibrated the full details of which are contained elsewhere and summarised in the in-flight calibration paper by Roelfsema et al (see [21]).

Further calibration information of use to users will also continue to be placed in a calibration page available via the Herschel Science Center website at

The HIFI calibration approach can be broken down into three main areas:

  • intensity calibration

  • frequency calibration

  • spatial response calibration

It is the combination of each of these three steps that provides the most accurately calibrated HIFI spectrum (see summary in section Section 5.5, “The Spatial Response Calibration of HIFI:”). For each of these areas, a framework document has been produced, describing in extensive details the calibration strategy and equations applying to HIFI. In the following, we summarise the content of this framework.