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Gas-Cell Simulator |  Atmospheric Paths |  My Spectra |  Line List Browser |  Blackbody Calculator |  Atmosphere Browser |  Solar Calculator |  Unit Converter

What's New at SpectralCalc

February 28, 2023
All HITRAN gases now available

The Gas Cell Simulator and Line List Browser tools now work with all available HITRAN gases (gas ids 1-55 for HITRAN 2020).

February 2, 2023
Added HITRAN 2020 linelist

The 2020 HITRAN line data is now available for use with the gases included in HITRAN 2008, (gas ids 1-42). This is now the default linelist for subscribers. HITRAN 2020 is described in: Gordon, I.E. et al., "The HITRAN2020 Molecular Spectroscopic Database", Journal of Quantitative Spectroscopy and Radiative Transfer, 107949, DOI 10.1016/j.jqsrt.2021.107949, 2021.

August 20, 2018
Added HITRAN 2016 linelist

The 2016 HITRAN line data is now available for use with the gases included in HITRAN 2008, (gas ids 1-42). HITRAN 2016 is described in: Gordon, I.E. et al., The HITRAN2016 molecular spectroscopic database, JQSRT, 203, 3-69, doi:/10.1016/j.jqsrt.2017.06.038, 2017.

April 28, 2015
Updated water continuum model

Model updated to use coefficients derived from 2.5.2 MT_CK: Mlawer, E. J., V. H. Payne, J.-L. Moncet, J. S. Delamere, M. J. Alvarado and D. D. Tobin, Development and recent evaluation of the MT_CKD model of continuum absorption, Phil. Trans. Roy. Soc. A, 370, 1-37, doi:10.1098:rsta.2011.0295, 2012.

April 27, 2015
Added HITRAN 2012 linelist

The 2012 HITRAN line data is now available for use with the gases included in HITRAN 2008, (gas ids 1-42). Note that the 727 isotope of CO2 is now isotope 9 and the 838 isotope has been removed due to limit of 9 isotopes in the current version of SpectralCalc. HITRAN 2012 is described in: Rothman, L.S. et al., The HITRAN2012 molecular spectroscopic database, JQSRT, 130, 4-50, doi:10.1016/j.jqsrt.2013.07.002, 2012. This update also includes use of the 2011 Total Internal Partition Sums (TIPS) data, decribed in: Laraia, A.L., Robert R. Gamache, Julien Lamouroux, Iouli E. Gordon, and Laurence S. Rothman, Total Internal Partition Sums to Support Planetary Remote Sensing, Icarus, 215, 391- 400. DOI: 10.1016/j.icarus.2011.06.004, 2011.

May 2, 2013
Modeling of UV-Vis Ozone

We've added the capability to simulate ozone absorption and emission at UV, visible, and near IR wavelenths (213 - 995 nm or 10,050 - 46948 cm-1). This will automatically be applied to any simulation (gas cell or atmospheric path) including ozone in this spectral region. No additional inputs are required.

December 20, 2012
My Spectra Tool

We've added a "Scale" tool to the My Spectra toolbox. This option lets you multiply any of your saved spectra by a constant value. This is very useful in, for example, situations where you want to simulate a constant attenuation across the spectrum. As part of this upgrade, we've also relaxed the minimum number of points required in an uploaded/saved spectrum from 6 to 3. Now it's super easy to upload a synthetic spectrum made "by hand" in a text editor. See the My Spectra help page for more details.

February 28, 2012
Custom Atmospheres

Now you can upload your own atmosphere with our newly designed Atmosphere Browser tool. Create your own custom atmospheric models in seconds and immediately use them in simulations. Want to run a simulation using a temperature profile from a third party? No problem, just upload the data! Modify the vertical profile of any species simply by uploading your own, easily formatted text file. We’ve also redesigned the interface to make viewing and extracting the data from atmospheres quicker and easier than ever. Custom atmospheres for both Earth and Mars are supported with this release. For more details, visit the Atmosphere Browser or documentation.

September 7, 2011
Abundance Scaling of Species

Gas Cell calculations for individual isotopologues now use the VMR exactly as specified. Previously, we scaled the VMR of individual isotopologues by their natural abundance. Simulations of “All” isotopologues have not changed, where we simulate a mixture of all individual isotopologues with concentrations in proportion to their natural abundances. (Atmospheric path calculations are not affected by this update.)

We’ve also added two new features to the LineList Browser. 1) The line intensities can now be scaled by the atmospheric concentration of the species. This gives a better picture of the relative importance of multiple species when dealing with atmospheric applications. 2) Line intensities of individual isotopologues can now be displayed with or without the built-in natural abundance scaling.

May 6, 2011
Default Blackbody Source

We've updated the default setting of radiance calculations. All radiance simulations now include only the radiance of the atmospheric path or gas-cells by default. Background source radiance can be included explicitly by using the Source tab. There you can adjust the temperature and emissivity of the source. This makes the default behavior consistent for gas-cell simulations and the various atmospheric path scenarios.

April 21, 2011
Atmospheric Temperature Offsets

You can now adjust the temperature of an atmospheric path! This can be very useful in studying the sensitivity of spectra to atmospheric temperature. The offset is applied to all altitudes, and the pressures are adjusted so that they remain in hydrostatic balance, tied to the surface pressure of the model atmosphere. (Offsets are limited to -50 to +50 K, and can be applied to any path through any atmosphere, even Martian simulations).

December 8, 2010
Instrument functions in My Spectra

Instrument functions (sometimes called apodization or smoothing functions) can now be applied to any of your saved spectra. This brings a new level of power to the My Spectra tools. Previously, instrument functions had to be specified before calculating a spectrum. Now you can apply your choice of instrument functions to any saved spectrum. Smoothed spectra can then of course be re-stored and even re-smoothed!

August 25, 2010
Zoom capability for My Spectra

Plotting your saved spectra using the My Spectra Tool is now even more powerful. In addition to controlling the spectral range (x-axis range) that is displayed, we've added the capability to specify the y-axis range. This allows you to zoom in on small features in the spectra, or use a consistent scale over multiple plots.

July 13, 2010
Improved interface for Mars Atmosphere

Access to the Mars atmosphere simulations is simplified with our new interface. To switch between Mars and Earth atmospheres, simply click on the picture of Earth or Mars on the Atmosphere tab.

May 27, 2010
Absorption Plots

You can now calculate absorption spectra, in addition to transmittance and radiance. Plotting the absorption (1 – transmittance) is particularly useful when the transmittance is very near 1. Absorption spectra can be plotted on either linear or log scales.

May 13, 2010
Martian Atmosphere

We’ve added a complete atmospheric model for Mars, including vertical profiles of 9 species, temperature and pressure. Atmospheric Path calculations accurately account for Mars’ smaller radius as well as the lower pressure, carbon dioxide rich atmosphere. View the Mars vertical profiles from the Atmosphere Browser, and perform simulations from the Atmospheric Paths tool. Simply select “Martian Standard” from the Model Atmosphere menu.

April 21, 2010
Atmospheric Paths Are Here!

Full atmospheric path modeling is now available! Simulate any geometry: horizontal, slant paths or limb paths. Choose your waveband and path geometry, and press Calculate! It’s that simple. Select a model atmosphere from our database, and adjust individual gas concentrations as desired. Click here to try it out. Documentation is available here.

March 12, 2010
Continua Models for N2, O2 and H2O

Correction: The notice dated June 12, 2009 incorrectly stated that all spectra would contain the continuum models, as needed. However, continuum effects are included only in gas-cell simulations, not in atmospheric path spectra.

February 15, 2010
Adjust vertical scaling for saved spectra

You can now control the scale of the y-axis when viewing saved spectra (on the My Spectra Tool). This allows you to see small absorption features that might not be easily visible when the plot is auto-scaled, or create multiple plots with consistent scales.

Oct 14, 2009
Sorting of My Spectra

Organizing your spectra is even easier now, with the new sorting utility. Clicking on any heading (Name, Lower Limit, Upper Limit, Points, Type, Date) in the My Spectra tool will sort all your spectra by that parameter. Clicking again will reverse-sort by that parameter.

Oct 1, 2009
Average Values

The average value is computed and printed on every plot created with the My Spectra tools. This includes plots with user-specified spectral ranges, difference plots, and plots of products or sums. Difference plots now include both the average and RMS difference, computed only within the plotted spectral range. [Example]

Sept 23, 2009
Difference-order on My Spectra

Users can now specify the order in which difference spectra are computed. This allows users to maintain consistency when collecting and comparing many different plots from various spectra saved in their My Spectra tool.

Sept 18, 2009
HITRAN update for C2H6 (ethane)

Line parameters for a second ethane isotopologue, (13)C(12)CH6, have been added to the HITRAN2008 database. The new data have been uploaded, and all calculations using HITRAN 2008 from now on will be made with these new line parameters. [Example] [More details]

Aug 11, 2009
Save Atmospheric Path Setups

Users can now save the settings of any atmospheric path calculation. Similar to the Gas Cell Calculator, all parameters are stored in the My Settings tab on the Atmospheric Paths tool. This allows you to recall and repeat calculations without having to retype the information, and provides an excellent for record-keeping.

Aug 5, 2009
Dots-only Plots on Linelist Browser

We added another plot option for graphing the line intensities in the Linelist Browser: dots without sticks. Previously, the only options were to plot the intensities as plain sticks or as sticks with dots. Now we've added a third option, dots without sticks [Example].

July 23, 2009
OCS line parameter update

Updated OCS line parameters from HITRAN have been released. Broadening parameters and line intensities of all OCS isotopologues are affected. The new data have been uploaded, and all calculations using HITRAN 2008 from now on will be made with these new line parameters. [Example plot] [More details]

July 2, 2009
Update to HITRAN 2008 H2O

The HITRAN committee has released an update to the water vapor line parameters. This update affects the line intensities of the HDO water vapor isotopologue at wavenumbers above 11,500 cm-1. The new line parameters have been ingested into our database, and all calculations using HITRAN 2008 from now on will be made with these new line parameters. [Example plot] [More details]

June 29, 2009
New website design

We've completely overhauled the look-and-feel of the website. With the addition of so many spectral modeling tools, the existing layout was becoming too complicated for new users. We created a new top-level design to make transition between the various tools faster, easier and more intuitive. The underlying calculations are unchanged, and accurate results are still our number one priority.

June 12, 2009
Continua Models for N2, O2 and H2O

Continuum absorption/emission effects for N2, O2 and H2O are now automatically included as needed for all Gas Cell and Atmospheric Path simulations. These continuum models augment the standard “line-by-line” calculation, more accurately accounting for far-wing effects at high pressures.

For O2 and N2, the spectral ranges affected are 1345-1820 cm-1 and 2105-2620 cm-1, respectively. The H2O continuum is significant at wavenumbers below 600 cm-1 and between 1200 and 2000 cm-1. For all three gases, the effect is proportional to pressure, and is negligible at pressures less than ~10 mbar.

Spectra for these gases in these spectral ranges calculated prior to this update did not include continuum effects, and should be recalculated with the new version. [more details]
Correction: please see March 12, 2010 entry.

May 25, 2009
HITRAN 2008 data released

The 2008 edition of the HITRAN data were released this earlier this month, and these data are now available on spectralcalc.com for download, display and for use in spectral simulations. The HITRAN 2004 data will remain available indefinitely, and will be the default for public use, but we recommend using the new HITRAN 2008 data wherever possible.

To assess the impact of the new data on your earlier results, you can easily compare the datasets using the Line List Browser or by simulating spectra with each, saving them, and using the My Spectra tool to view the residual difference.

Apr 22, 2009
Major Update to Website

We've completely updated our website, and added several important new capabilities. Highlights include:

Atmospheric Paths
With the "Atmospheric Path" tool, you can now simulate accurate molecular transmittance and/or emission spectra for paths through the Earth's atmosphere. Begin by choosing from a list of model atmospheres and, if needed, tailor the concentrations of absorbing gases to your specific application. As of now, both horizontal and vertical paths are supported, and developers are putting the finishing touches on the more general slant-path geometries. These are the same models used by NASA and Universities worldwide in space-based atmospheric science missions.

My Spectra Tool
Subscribers now have the option of saving spectra from any of their calculations, or uploading their own spectra, whether lab, field or model based. Spectra can be compared, multiplied (transmittance) or summed (radiance). Plots of the residual differences between two spectra can help you quickly isolate regions of interest. Interpolation and resampling are handled quickly and efficiently behind the scenes, so the user doesn't have to contend with these time-consuming tasks. This is an invaluable tool for spectroscopic research.

Group Account Tools
Group subscriptions can now be purchased online and administered instantly, without any need for email or phone support. Administrators can manage their group account from the "My Account" link. Here you will see a list of all users currently in the group. You can add or delete users, and can designate an additional administrator if desired. Users can also join the group by logging in and entering the group code in "My Account".

Gas-cell Simulator
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Other browsers may work but are not fully tested or supported.
Transmittance: ratio of received radiation intensity, I, to incident light intensity, I0

Transmittance: ratio of received radiation intensity, I, to incident light intensity, I0

The information provided will not be shared, sold or used in any way other than to contact users to announce new features.
Radiance: radiant flux radiated per unit area, per unit solid angle, per wavenumber

light with wavenumber between σ and σ + dσ
Radiance: radiant flux radiated per unit area, per unit solid angle, per wavenumber

light with wavenumber between σ and σ + dσ
Isotopes are forms of an element whose nuclei have the same atomic number, the number of protons in the nucleus,but different atomic masses because they contain different numbers of neutrons.
Cell: model the transmission/radiance of a gas cell. Specify it's length, temperature and pressure, and the vmrs of the absorbing gases.

Wavenumber cm-1: the number of
wavelengths of light per centimeter

LINEPAK: The GATS spectral radiance and transmission software library. Performs detailed and accurate line-by-line modeling of molecular absorption. Efficient and flexible, LINEPAK is at the heart of analysis systems for many major atmospheric remote sensing missions, including HALOE, SABER, LIMS, SOFIE, CRISTA, and CLAES.
Tangent Path: Model the transmission or radiance of a ray that passes completely through the Earth's atmosphere but does not intersect the Earth. The path is specified by the tangent height, the height at the point of closest approach to the surface. The pressure, temperature and vmrs of absorbing gases at each altitude are chosen from a database of atmospheric states.
Slant path: Model the transmission or radiance of a ray between two arbitrary points in the Earth's atmosphere. The points are specified by their heights and the zenith angle from one to the other.
VMR: volume mixing ratio. The fractional number of molecules of a species in a volume.

Individual vmrs and their sum must be between 0 and 1.

If the vmrs sum to less than 1, the rest of the gas in the cell is assumed transparent.(Lineshapes for molecules with vmr less than 1 are air-broadened.)
Clicking this will display the data as text in a new browser window. Right-clicking will download the data file to your computer (recommended). These files can be extremely large depending on the spectrum simulated.
Clicking this will open a new browser window suitable for printing.
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To help ensure the availability of our servers, public use is limited to 50 calculations per day. Subscribe now for uninterrupted service. Subscribers also have access to advanced features such as large wavebands, multiple gases, choice of units, radiance spectra, logo-free high-resolution graphics, ascii data files,
full tech support and much more.


Spectroscopy and remote sensing tools for researchers, teachers, and students

Subscribe now for full access to the Spectral Calculator tools.

Get priority use of advanced, state-of-the-art radiative transfer algorithms--the same ones used by NASA for many remote sensing missions. Subscribers gain access to large wavebands, multiple gases and cells, choice of units, radiance spectra, logo-free high-resolution graphics, data files, full tech support, and much more.


Temperature Offset: The model atmosphere (US_Standard, Tropical, etc.) determines the temperature, pressure and gas concentrations at each height in the atmosphere. To adjust the temperature from the model value, enter a temperature offset (from -50 to 50 K). The Atmosphere Browser tool displays the temperature profiles for the model atmospheres.
Atmosphere: An atmosphere contains profiles of temperature and gas concentrations at all altitudes. There are six system-supplied atmospheres for Earth and one for Mars. Custom atmospheres can be uploaded from the Atmosphere Browser.
Scale Factor for Gas Concentrations: The model atmosphere (US_Standard, Tropical, etc.) determines the gas concentrations at each altitude. To adjust a gas concentration, choose a scale factor, from 0 to 1000. For example, to simulate an atmosphere with 20% more water vapor than the model, enter a scale factor of 1.2 for H2O. Note: while the model atmospheres are physically realistic, using large scale factors can produce unphysical situations where the gas abundance exceeds 100%. If this occurs, an error message will be displayed.
The atmosphere model (US_Standard, Tropical, etc.) determines the temperature, pressure and gas concentrations at each height in the atmosphere. To adjust a gas concentration, choose a scale factor other than 1 (from 0 to 1000). For example, to simulate a path with 20% more water vapor, use a scale factor of 1.2 for H2O. The Atmosphere Browser tool displays the temperature, pressure and gas mixing ratios for the model atmospheres..
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