ESA Earth Home Missions Data Products Resources Applications
EO Data Access
How to Apply
How to Access
MIPAS Data Formats Products
2 MDSR per MDS 1 forward sweep 1 reverse sweep
2 MDSRs per MDS 1 forward sweep 1 reverse sweep
LOS calibration GADS
Spectral Lines MDS
P T Retrieval MW ADS
VMR Retrieval Parameters GADS
P t Retrieval GADS
Framework Parameters GADS
Processing Parameters GADS
Inverse LOS VCM matrices MDS
General GADS
Occupation matrices for vmr#1 retrieval MDS
MDS2 -- 1 mdsr forward sweep 1 mdsr reverse
Occupation matrices for p T retrieval MDS
General GADS
Priority of p T retrieval occupation matices
P T occupation matrices ADS
Summary Quality ADS
Instrument and Processing Parameters ADS
Microwindows occupation matrices for p T and trace gas retrievals
Scan information MDS
Level 2 product SPH
MDS1 -- 1 mdsr forward sweep 1 mdsr reverse sweep
H2O Target Species MDS
P T and Height Correction Profiles MDS
Continuum Contribution and Radiance Offset MDS
Structure ADS
Summary Quality ADS
Residual Spectra mean values and standard deviation data ADS
PCD Information of Individual Scans ADS
Instrument and Processing Parameters ADS
Microwindows Occupation Matrices ADS
Scan Information MDS
1 MDSR per MDS
Scan Geolocation ADS
Mipas Level 1B SPH
Calibrated Spectra MDS
Structure ADS
Summary Quality ADS
Offset Calibration ADS
Scan Information ADS
Geolocation ADS (LADS)
Gain Calibration ADS #2
Gain Calibration ADS #1
Level 0 SPH
DSD#1 for MDS containing VMR retrieval microwindows data
DSD for MDS containing p T retrieval microwindows data
VMR #1 retrieval microwindows ADS
P T retrieval microwindows ADS
1 MDSR per MDS
VMR profiles MDS (same format as for MIP_IG2_AX)
Temperature profiles MDS (same format as for MIP_IG2_AX)
Pressure profile MDS (same format as for MIP_IG2_AX)
P T continuum profiles MDS (same format as for MIP_IG2_AX)
GADS General (same format as for MIP_IG2_AX)
Level 0 MDSR
Values of unknown parameters MDS
Computed spectra MDS
Jacobian matrices MDS
General data
Data depending on occupation matrix location ADS
Microwindow grouping data ADS
LUTs for p T retrieval microwindows MDS
GADS General
P T retrieval microwindows ADS
ILS Calibration GADS
Auxilliary Products
MIP_MW1_AX: Level 1B Microwindow dictionary
MIP_IG2_AX: Initial Guess Profile data
MIP_FM2_AX: Forward Calculation Results
MIP_CS2_AX: Cross Sections Lookup Table
MIP_CS1_AX: MIPAS ILS and Spectral calibration
MIP_CO1_AX: MIPAS offset validation
MIP_CL1_AX: Line of sight calibration
MIP_CG1_AX: MIPAS Gain calibration
MIP_SP2_AX: Spectroscopic data
MIP_PS2_AX: Level 2 Processing Parameters
MIP_PS1_AX: Level 1B Processing Parameters
MIP_PI2_AX: A Priori Pointing Information
MIP_OM2_AX: Microwindow Occupation Matrix
MIP_MW2_AX: Level 2 Microwindows data
MIP_CA1_AX: Instrument characterization data
Level 0 Products
MIP_RW__0P: MIPAS Raw Data and SPE Self Test Mode
MIP_NL__0P: MIPAS Nominal Level 0
MIP_LS__0P: MIPAS Line of Sight (LOS) Level 0
Level 1 Products
MIP_NL__1P: MIPAS Geolocated and Calibrated Spectra
Level 2 Products
MIP_NLE_2P: MIPAS Extracted Temperature , Pressure and Atmospheric Constituents Profiles
MIP_NL__2P: MIPAS Temperature , Pressure and Atmospheric Constituents Profiles
Glossaries of technical terms
Level 2 processing
Miscellaneous hardware and optical terms
Spectrometry and radiometry
Data Processing
Alphabetical index of technical terms
Frequently Asked Questions
The MIPAS Instrument
Inflight performance verification
Instrument characteristics and performances
Preflight characteristics and expected performances
Subsystem description
Payload description and position on the platform
MIPAS Products and Algorithms
Data handling cookbook
Characterisation and calibration
Latency, throughput and data volume
Auxiliary products
Level 2
Instrument specific topics
Algorithms and products
Level 2 products and algorithms
The retrieval modules
Computation of cross-sections
Level 1b products and algorithms
Calculate ILS Retrieval function
Level 1a intermediary products and algorithms
Product evolution history
Definition and convention
MIPAS Products User Guide
Image gallery
Further reading
How to use MIPAS data?
Summary of applications and products
Peculiarities of MIPAS
Geophysical coverage
Principles of measurement
Scientific background
MIPAS Product Handbook
Site Map
Frequently asked questions
Terms of use
Contact us


5.3.2 Spectrometry and radiometry

MIPAS detectors are combined in five spectral bands. The table below gives the detectors configuration and the spectral range of these bands.
Table 5.1
Band Detectors Spectral range (cm-1)
A A1 and A2 685 - 970
AB B1 1020 - 1170
B B2 1215 - 1500
C C1 and C2 1570 - 1750
D D1 and D2 1820 - 2410


In MIPAS, the beamsplitter is a plate of transparent material with optical coatings designed to reflect 50% of the incoming infrared radiation and let the remaining fraction goes through. In other words, it is a semi-transparent mirror.
An ideal body that completely absorbs all radiant energy striking it and, therefore, appears perfectly black at all wavelengths. The radiation emitted by such a body when heated is referred to as blackbody radiation and is given by the Planck's equation. Black body radiation is only function of the temperature of the black body emitting it. Almost ideal blackbodies are often used as reference sources in infrared radiometry.
Radiometric calibration is the process by which physical units are attributed to the raw spectrum derived from the measured interferograms. The radiometric calibration is applied as follow:

L = G xeq 5.1
FFT{I - Io } = G x (S - So )

where L is the calibrated radiance, G is the radiometric gainS is the raw spectrum to calibrate and I is its correspondin interferogram, Io is the interferogram acquired while looking at the deep space (offset measurement ) and So is its corresponding raw spectrum.
Click here for details.

Spectral calibration is the process by which the wavenumber of every point of the spectrum are validated and corrected if necessary. Spectral calibration is done by verifying the spectral position of reference atmospheric lines. Click here for details.

Cube corner retro-reflectors:

A cube corner retro-reflector is made of three perpendicular flat mirrors. Any ray of light that strikes the inside of the cube corner is reflected in the same direction that it came.
The act of systematically rejecting points at given intervals in the interferogram. Decimation is used to reduce the data rate. The decimation factor is the integer ratio of the initial sampling frequency to the new one. Decimation factors are programable. The following table list the nominal decimation factors for the bands of MIPAS:
Table 5.2
Band Detectors Decimation factor
A A1 and A2 21
AB B1 38
B B2 25
C C1 and C2 31
D D1 and D2 11
Doppler shift:
A spectral shift of the observed radiation as a result of the Doppler effect. The Doppler effect is due to a relative motion between the source and the observer. The radiation emitted from a source that moves away from an observer appears to be of lower frequency than the radiation emitted from a stationary source. The radiation emitted from a source moving toward the observer appears to be of a higher frequency than that from a stationary source. For MIPAS, the Doppler shift is caused by the relative motion between ENVISAT and the atmosphere.
The random relative motion of the atmospheric molecules causes a broadening of the atmospheric spectral lines, called Doppler broadening.  Since the relative motion of the atmospheric molecules depends on pressure and temperature, the importance of the Doppler broadening contains information about the altitude and the temperature of the air.
In MIPAS 5.1. the radiometric gain, G, is computed as follow:

G = Lbb / (eq 5.2
FFT{Ibb - Io }) = Lbb / (Sbb - So )

where Lbb is the theoretical radiance of the calibration blackbody. Ibb is the interfeogram acquired while looking at the calibration blackbody (gain measurement), Io is the correspomding raw spectrum, Io is the interferogram acquired while looking at the deep space (offset measurement ) and Io is the corresponding raw spectrum. See radiometric calibration.

The ratio of an object's radiance to that emitted by a blackbody radiator at the same temperature and at the same wavelength. A perfect blackbody has an emissivity of 1.
Exitance is the amount of radiant flux emitted by a source per unit source area. It is the surface density of power on a source. It depends only on the source. For example a spherical source with a radius of 1 cm that emits a radiant flux of 10 W has an exitance of 10 W divided by the surface (4 pi times 1 cm2) or 25000 W m-2.


Radiant flux (also called radiant power) is the amount of energy emitted by a source or received by a detector per unit time. For example if a source emits 100 Joules of radiant energy in 10 seconds, its radiant flux is 10 Watt.
Instrumental line shape:
The instrumental line shape (or ILS) is the unapodised instrumental response to a stimulus of negligible spectral width. The ILS varies as a function of the wavenumber. The ILS also determines the spectral resolution of the instrument.

Figure 5.1


Intensity is the amount of radiant flux radiating in a given direction per unit solid angle. For example an isotropic source that emits a radiant flux of 10 Watt has an intensity of  10 W divided by the solid angle of sphere (4 pi steradians) or 0.8 W sr-1 in any direction and at any distance from the source.


The additive process whereby the amplitudes of two or more overlapping radiation beams are systematically attenuated and reinforced.


Photographic or electronic recording of an interference pattern.
Figure 5.2

A typical interferogram Click here to see a simulated inteferogram of MIPAS.


Irradiance is the amount of radiant flux received by a surface perpendicular to the incident radiation per unit area of the surface.

Maximum path difference:

Maximum path difference (MPD) is the maximum distance between a mirror and ZPD. It is half the maximum effective distance between the two mirrors of the interferometer. For MIPAS, the MPD is 20 cm.
Noise Equivalent Spectral Radiance:
The noise equivalent spectral radiance (NESR) is the rms noise of a given measurement expressed in unit of radiance.
Radiance is the amount of radiant flux propagating in a given direction per unit area and unit solid angle. It is the most general radiometric quantity. It is used to describe both emitted and received radiation.

Radiometric quantity:

The various quantities used in radiometry to quantify radiation. The usual radiometric quantities, the symbols used in this document to describe them and their SI units are given in the following table:
Table 5.3
Radiometric quantity Symbol Units
Energy Q J
Power, flux F W
Exitance M W m-2
Irradiance E W m-2
Intensity I W sr-1
Radiance L W m-2 sr-1
Spectral radiometric quantity are given per unit wavelength or per unit wavenumber.


The science interested by the detection, measurement and quantification of electro-magnetic radiation in terms of energy.
Signal to noise ratio:
Signal to noise ratio is the signal divided by the noise, both quantities being given in the same units. It gives the relative importance of the measured signal compared to the noise in the measurement.

Spectral binwidth:

The spectral binwidth or spectral interval is the difference along the spectral axis between two consecutive points in a spectra. This is to be distinguished from the spectral resolution. The spectral interval in wavenumber units of spectra generated by a given Fourier transform spectrometers is a constant and is given by 0.5 / MPD.

Spectral resolution:

Spectral resolution determines the ability of the instrument to distinguish closely spaced spectral features. An instrument cannot distinguish two spectral features that are closer than its spectral resolution. Spectral resolution is usually determined by the full width at half maximum of the instrumental line shape.Spectral resolution is often confused with spectral bindwidth.
An instrument that is calibrated so as to measure radiation (energy) amplitude as a function of wavelength.
A curve that shows a spectral radiometric quantity as a function of wavelength (or wavenumber).

Figure 5.3

A typical atmospheric spectrum

Click here to see a simulated MIPAS spectrum.
Recording for a single interferogram. A sweep can be forward or reverse. The adjective forward or reverse are attributed to the sweep depending on the direction of motion of one of the cube corner of the interferometer.


In spectroscopy, the wavenumber is the inverse of the wavelength. In infrared spectroscopy it is customary to express the wavenumber in cm-1. Wavenumbers are preferred to wavelengths in Fourier transform spectroscopy because  the spectra measured by such instruments are of constant step size (along the spectral axis) when expressed in wavenumbers.
Zero Path Difference:
The expression "Zero path difference" or ZPD is used to describe the location of the moving mirrors such that the two arms of the interferometer are of equal optical path length. At ZPD, the interference is constructive for every wavelengths and the interferogram is at its absolute maximum in one of the output port (and thus at its absolute minimum in the other output port).

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry