A practical guide to IR and MW radiative transfer using the RTTOV model and GUI Practical exercises

Start up the RTTOV GUI type: rttovgui Class01,trd00, 2tDQohR,

Exercise #1 – run RTTOV direct model for AMSU-A MW sounder File/Open Profile to select and Open Diverse_profile_set.h5 and select profile 1. RTTOV/Load Coefficients to Choose and Open and Load AMSU-A RTTOV coefficients rtcoef_metop_2_amsua.dat from coefficients directory RTTOV/Run RTTOV direct to run the direct model. The Radiance Viewer is displayed showing the brightness temperature in each AMSU-A channel. Windows/Surface Editor Window to view surface and other input variables. Modify skin temperature. RTTOV/Run RTTOV direct to run the direct model again (do not close the Radiance Viewer window between runs!) In the Radiance Viewer select --Pseudo run--/run_02 minus run_01 to see the difference. Windows/Profile Editor Window to view temperature and gas profiles. Modify temperature profile near the tropopause (~50-200hPa). RTTOV/Run RTTOV direct to run the direct model again (do not close the Radiance Viewer window between runs!) In the Radiance Viewer select --Pseudo run--/run_03 minus run_02 to see the difference.

GUI main control window

GUI pull down menus

Open a profile

Open a profile

Open a profile

Open a profile Select Diverse_profile_set.h5

Open a profile

Open a profile Select profile 1 from the list

Open a profile

Choose and Load AMSUA (RT) coefficients

Choosing (RT) coefficients

Choosing (RT) coefficients

Choosing (RT) coefficients

Choosing (RT) coefficients

Choosing (RT) coefficients

Loading (RT) coefficients

Run RTTOV direct

Radiance Viewer – Overview (Some options will make more sense in a moment after running more simulations – don’t close the Radiance Viewer window!) Select between brightness temperature and radiance Plot results for a single channel for all runs performed so far. Choose which run to display (after doing multiple simulations) Plot differences between runs or compare two runs on the same plot Choose which run is the reference for the “Pseudo run” comparisons By default plot shows brightness temperatures in each channel for the most recent simulation performed.

Open Surface Editor Window

Modify Skin Temperature to 330K

Apply the change

Re-run RTTOV direct (Don’t close the Radiance Viewer between runs!)

In Radiance Viewer plot difference between the two runs

In Radiance Viewer plot difference between the two runs The differences are shown in red. The scale is on the right side of the plot. Notice which channels show a change in brightness temperature and which show no change. Compare this with the weighting functions plotted on the following two slides.

AMSU-A weighting functions for a selection of surface-sensitive channels

AMSU-A weighting functions for a selection of channels insensitive to the surface

Open Profile Editor Window

Profile Editor Window - Overview After making changes select Apply change in File menu Undo/Redo and other editing options available in Edit menu View temperature and gas profiles individually using the tabs Right-click in this window to modify profile values on individual levels All input profiles are shown together here NB ozone and CO2 profiles are ignored for MW simulations Select the zoom tool and drag a box on the plot to enlarge an area

Edit temperature profile near tropopause Ensure Temperature tab is selected here

Edit temperature profile near tropopause Edit values to scale temperature profile by a factor of 1.05 between pressure levels of 50 and 200hPa then select OK

Apply the change

Re-run RTTOV direct (Don’t close the Radiance Viewer between runs!)

In Radiance Viewer plot difference between the last two runs

In Radiance Viewer plot difference between the last two runs Again notice which channels show the largest changes. Those channels whose weighting functions peak within or near the 50-200hPa region show the largest BT differences (see next slide). Other channels show limited sensitivity to the temperature change.

AMSU-A weighting functions for a selection of channels insensitive to the surface

Exercise #2 – run RTTOV direct and K models for IASI high resolution IR sounder File/Open Profile to select and Open Diverse_profile_set.h5 and select profile 52. RTTOV/Load Coefficients to Choose and Open and Load IASI RTTOV coefficients rtcoef_metop_2_iasi.dat from coefficients directory. Windows/Options Editor Window to view RTTOV configuration options. Ensure “ozone_data”, “switchrad” options are checked. Windows/Surface Editor Window to view surface and other input variables. Ensure surface type is set to Land. RTTOV/Run RTTOV direct to run the direct model. The Radiance Viewer is displayed showing the IASI brightness temperature spectrum. Windows/Profile Editor Window to view temperature and gas profiles. Modify ozone profile. RTTOV/Run RTTOV direct to run the direct model again (do not close the Radiance Viewer window between runs!) In the Radiance Viewer select --Pseudo run--/run_02 minus run_01 to see the difference which highlights which parts of the IASI spectrum are sensitive to ozone. RTTOV/Run RTTOV K to run the K model. Examine some individual Jacobians in different parts of the spectrum using the “kP” button.

Open a profile

Open a profile

Open a profile

Open a profile Select Diverse_profile_set.h5

Open a profile

Open a profile Select profile 52 from the list

Open a profile

Choose and Load IASI (RT) coefficients

Choosing (RT) coefficients

Choosing (RT) coefficients

Choosing (RT) coefficients

Choosing (RT) coefficients

Choosing (RT) coefficients

Loading (RT) coefficients rtcoef_metop_2_iasi.dat

Open Options Editor Window

Open Options Editor Window ozone_data – enables ozone as a variable gas in the simulations. switchrad – Jacobians are calculated with respect to BT (if true) rather than radiance (if false). Ensure “ozone_data” and “switchrad” options are checked and then click “Apply”.

Open Surface Editor Window

Modify SURFTYPE to Land

Apply the change

Run RTTOV direct

Run RTTOV direct Hover mouse cursor over plot to display channel number, wavenumber/wavelength and simulated BT

Open Profile Editor Window

Edit ozone profile Ensure Ozone tab is selected here NB For this coefficient file CO2 is not active as a variable trace gas

Edit ozone profile Edit value to scale the entire ozone profile by a factor of 1.05 then select OK

Apply the change

Re-run RTTOV direct (Don’t close the Radiance Viewer between runs!)

In Radiance Viewer plot difference between the two runs

In Radiance Viewer plot difference between the two runs Main ozone band is around 9.5µm (~1050cm-1)

Run RTTOV K

K Matrix Viewer - Overview Scroll left/right by one page Scroll left/right by 80 channels Plot Jacobians for a specific channel Hover mouse cursor over each plot to display detailed information in status bar

Display Jacobians for ch1640 (ozone channel)

Display Jacobians for ch1640

Display Jacobians for ch1640 View temperature and gas Jacobians individually using the tabs All Jacobians are shown together here NB CO2 is not an active gas for this coefficient file This channel is insensitive to water vapour Skin temperature Jacobian

Display Jacobians for ch1640 The ozone Jacobian is negative i.e. increasing the ozone concentration decreases the satellite-seen radiance. Can you explain why the ozone Jacobian is negative in the troposphere, but close to zero in the stratosphere? Hint: consider the temperature profile and what would happen in terms of absorption and emission if the ozone concentration were increased at different pressure levels.

Plot the Jacobians for some other channels For example: ch3500 water vapour channel, similar to the ozone case ch94 CO2 channel, this band can be used for temperature sounding If you have time you can also run the Jacobian model for the AMSUA coefficient file