Radiannet is a two-band radiation simulation model. Retrievals of the physical properties of volcanic clouds are processed by adjusting the optical and physical parameters in the radiative transfer models to best fit the observed radiances. In the current program, AVHRR Band 4 and Band 5 brightness temperatures are simulated. The assumptions for using this program are:
Radiannet is composed of many different FORTRAN and IDL subroutines. An IDL widget interface is used to make entering the input parameters easy. The IDL code spawns FORTRAN subroutines, which does the radiative transfer calculations. The results of the calculations are stored in ASCII files. The IDL code reads these files and produces output plots.
For information on the basic theory behind the Radiannet Program see "Retrieval of sizes and total masses of particles in volcanic clouds using AVHRR bands 4 and 5" by Shiming Wen and William I. Rose in Journal of Geophysical Research, VOL. 99, NO. D3, Pages 5421-5431, March 20, 1994.
For information on the detection of volcanic clouds using AVHRR see .
The Radiannet code requires IDL to run. The code was developed using IDL version 3.6.1 but should run under IDL version 3.0 and later. The memory and disk space requirements depend on the size of the ASCII Input Data File. To analysis a typical volcanic cloud would require about 3 Mbytes of disk storage. So far the code has been tested on SUN workstation running SunOs 4.1.3 and Solaris 2.0. The FORTRAN codes were complied under SunOs 4.1.3. The Radiannet code would require minor changes to work on I.B.M. compatiables or Mac machines.
A Web Page Browser, such as Mosaic or Netscape, is required to read the help page. A printout of the help pages can by made for people without a Web Page Browser.
Terascan is a nice program to have when running Radiannet but is not essential. Terascan is used to generate the initial input file which contains the AVHRR band 4 and band 5 values, but this files could be generated any number of ways. Terascan is also useful to produce a really nice plot of the mass estimate, but Radiannet has a built in procedure to produce these plot also.
The model you select determines which FORTRAN program is executed. Note that not all function buttons and field parameters are used in each model. To run a model: 1) Select the model to run with the Model function button, 2) Make sure the function buttons and field settings are correct, 3) Click on the Execute/Plot button on the button left of the widget interface.
Band 4 and Band 4 minus Band 5 brightness temperature pairs are simulated for different particle radii and optical depth. The AVHRR data are fitted to this model by plotting the theoretical curves and the AVHRR Band 4 and Band 4 minus Band 5 brightness temperature. The Radius-Optical Depth Model is used to determine the value of the Cloud-Base temperature. The Cloud-Base temperature value should be adjusted until the data from the eruption fit into the theoretical curves. Note that the AVHRR data may not fit into the theoretical curves if the correct cloud aerosol type is not choosen.
The Range of Radius Model plots effective radius and normalized negative temperature domain areas. A discussion of the normalized area parameter is given in Wen and Rose (1194) on pages 5423-5424. It indicates the retrieval will work properly for particles with an effective radius over a range in which S si monotonically decreasing. This Range of Radius Model can be run serveral times to find a size range that will allow the retrievals to work.
The Radius-Optical Depth Model should be used in conjuction with the Range of Radius Model to determine the minimum and maxiumum radius which can be uniquely retrieved. The minimum and maximum radius depends on composition and size distribution of the aerosols.
This model is used to calculate particle radius, optical depth, and then retrieve the total mass retrieval. The Radius-Optical Depth and Range of Radius Models must be run first to determine the correct cloud-base temperature, minimum radii and maximum radii.
A uniform distribution assumes that all particles are the same size. The uniform distribution gives a lower bound on the volcanic cloud's mass estimate.
A gamma distribution can be used to describe the size distribution of water/ice clouds.
A volcanic cloud is considered to have a lognormal size distribution. Of the three particle distribution types considered, the lognormal size distribution gives the largest estimate of the volcanic cloud's aerosol mass.
The assumed type of aerosol in the volcanic cloud. The type of aerosol is determined from data of the ash fall out or in-situ aircaraft samples or by choosing the material type that produces the best fits to the theoretical curves in the Radius-Optical Depth Model. The type of material determines the refiractive index and the particle density to used in the radiative transfer calculations.
Display the plots on the Screen.
Creates a Postscript file in portrait mode. The file is saved with the filename "idl.ps" in the current directory. The utility function "Print PS" can be used to print the file.
Creates a Postscript file in Landscape mode. The file is saved with the filename "idl.ps" in the current directory. The utility function "Print PS" can be used to print the file.
Creates a Encapsulated Postscript file. The file is saved with the filename "idl.eps" in the current directory. This file can be imported into word processing programs like FrameMaker.
The type of symbol to use in the Radius-Optical Depth Plot.
This parameter is used only in the mass calulation. If Frame Scale Type is selected, the average particle radius for the whole frame is used as the effective radius for the mass calulation. If Pixel Scale Type is selected, the effective radius is different for each pixel in the frame. Note that for a lognormal distribution, only a Frame Scale Type can be selected. This is not much of a problem because usually only a small range of radii can be uniquely retrieved for a lognormal distribution.
If this button is set, labels are placed on the output plots
If this button is set, the input data file is assumed to contained latitude and longitude values.
This parameter is determined by running the Range Radius Model. The minimum and maximum radii values are used in the mass calulation.
This parameter is determined by running the Range Radius Model. The minimum and maximum radii values are used in the mass calculation.
The Cloud-Top Temperature can be determined by looking at the AVHRR band 4 temperature of the opaque part of the volcanic cloud. The opaque part of the volcani cloud is the optically thick part where the underling radiation does the pass through the cloud. The opaque part of the cloud is located nearest the volcanoe vent since large aresols have not fallen out yet.
The temperature at the base of the volcanic cloud. It can be determined by using the Radius-Optical Depth Model. The value is adjusted until the data from the eruption cloud fits into the theoretical curves the best.
The X dimension of the image. If the image is not a square image, the X should be set to the total number of pixels in the image and the Y dimension set equal to one.
The Y dimension of the image.
The area of one pixel of the volcanic cloud images. All pixels are assumed to have the same area.
The size of the plot symbol in the Radius-Optical Depth Model. The default size is one.
The spacing between the horizontal lines, usually optical depth lines.
This value is used to exclude the non-volcanic pixels from the calculation of the volcanic mass. Normally, a Band 4 - Band 5 temperature value greater than -0.5 is considered not to be a volcanic pixel. However, there is nothing special about -0.5 and this value may have to be adjusted for different volcanic clouds.
The number of vertical lines, usually optical depth lines.
The number of radii lines used in the model calulations.
This file contains AVHRR Band 4 Brightness Temperature and AVHRR Band 5 Brightness Temperature for each pixel in the volcanic cloud. The file can also include the latitude and longitude of each pixel. This file is a subset of a full AVHRR seen. Only the pixels that are believed to be a possible part of the volcanic cloud are included in this file. The ASCII Input Data File Name is the prefix for the output files created by Radiannet.
The settings for the IDL widget are saved in the binary file named "initial_setup_rad" each time you exit the Radiannet program.
The Total Mass of Particle Retrieval Model creates a file with the ".text" extention. This file contains the input parameters and results of the Total Mass of Particle Retrieval Model.
The Total Mass of Particle Retrieval Model creates a file with the ".mdr" extention. The ".mdr" file format is as folows: For each pixel in the image, the latitude and longitude on one line, followed by the total aerosol mass, optical depth, and effective radius on the next line.
This is a postscript file created by executing Radiannet with the Output function button selected to "PS Port" or "PS Land". This file can be printed by sending it to a postscript printer or by using the utility funtion "Print PS".
This is a encapsulated postscript file create by executing Radiannet with the output function button selected to "EPS". This file can be imported into a word processor such as Framemaker.
All the pixels in the image are assumed to have the same area. Therefore, it is important to use an equal area map projection for the input image. The IDL plot routine uses the Lambert's Equal Area Projection.
The first step is to register the image using a Master file that has an equal area projection such as the lambert_azim projection. The image needs to be subsetted so that it mostly contains volcanic cloud pixels. Using "xvu" (the terascan point-and-click interface), use the menu "Select" and select "Point Locations". Create a pointfile by outlinng the Volcanic pixels with "Outlines" or "Boxes". Make sure the Coordiantes type is "Lat/Lon". The easiest way to determine what are volcanic cloud pixels is by displaying Band 4 or by displaying Band 4 - Band 5. The pointfile can be displayed on an image by using xvu, use the menu "Overlay" and select "Points" and entering the pointfile name.
The next step is to create a subset outputfile. Using xvu, use the menu "Select" and select "Point List". For the file list, enter the registered image filename. Selected Band 4 and Band 5 variables. The pointfile is the filename of pointfile created in the previous step. Make sure that Save Corrds is "Yes".
The final step is to output the file in ASCII format. Using xvu, use the menu "Utils" and select "Export ASCII". The File list is the filename from the previous step. Selected all variables. Sort By "All Dims". Set List Dims to "NO"
A Radiannet input file can be created using an editor or image processing tools. A Radiannet Examples: Input and Output
