Wxsat is capable of producing APT images of considerable clarity and detail from both polar orbiting and geostationary satellites, and the software performs well under both Windows 3.x and Windows-9x. Wxsat comes complete with 16 pages of detailed documentation, which nevertheless leaves many features of its operation requiring lengthy experimentation to obtain the best results. This article sets out to ease the beginners initial foray into this field.
At this point, a word of caution. Wxsat makes heavy demands on your computer's CPU, and definitely requires a maths co-processor ( i.e. 486DX machine or better ). Additionally, because of these intense demands on processing capacity, you may not be able to take advantage of all wxsat's decoding modes. In fact, wxsat will not run at all in the absence of a co-processor. It is highly advisable to disable any screensaver in operation, since its activation frequently causes wxsat to crash.
If you run a more basic 486DX 33 MHz computer, its processor will not be able to keep up with the demands made on it, and the program will fail. But all is not lost. If you use your sound-card's own software to save the satellite audio signal as a wave ( .WAV ) file, you may subsequently use wxsat to decode the waveform into satellite images exactly as would happen during 'live' reception, though more slowly. Note that SX-type computers cannot run wxsat because they lack the necessary maths co-processor.
Another way around this problem is to make use of a program called "RECALL". This is activated by the audio signal from your soundcard, and has the sole function of saving signals as wave files. These files may subsequently be decoded into images by wxsat. ( Details in appendix B )
Make sure that the '16-bit audio' box is checked, and select the grey NOAA
button at top left to set up parameters to produce the familiar side-by-side
twin image format. Make sure that the 'GenCalibVar' and 'Lock' boxes are both
checked, then click the grey 'N-S' button at lower right as appropriate before
exiting with the 'OK' button. [ for the midday NOAA satellite, this should be
set to 'S-N'; for the morning satellite, N-S ] Select the
If all goes well, you should receive an image similar to the one above, which shows the two NOAA images side by side ( infrared on left, visible on right ).
The easiest way to configure wxsat's parameters is by firstly saving such a
NOAA transmission as a wave (WAV) file. Open the The
It is essential that the signal is as high as possible without breaching
either of these lines. This adjustment can be achieved using the software
supplied with your soundcard. Unfortunately, wxsat is highly sensitive to
multitasking, and frequently crashes if any other program operates
simultaneously, especially on slower computers.
A better solution is to insert a variable potentiometer into the external
audio feed connecting the weather satellite-receiver to the sound-card. This can
be adjusted quickly and efficiently without affecting the operation of wxsat.
Adjust the potentiometer until no peak in the display touches either the upper
or lower grey line - this takes but a few seconds. Return to the After reception of your image, examine the amplitude [upper] histogram.
This should sit squarely between zero and 1.00 on its horizontal axis. If it
does not, you must alter the 'BasicAmp' factor on the Parameter Window
to make it do so. Herein lies the value of saving the WAV file. By changing this
parameter, then decoding part of the WAV file again, the histogram may be
adjusted until the best possible fit has been achieved.
This done, the luminance [lower] histogram must also be adjusted to fit along
its horizontal axis in identical fashion, this time by making changes to the
'Ampl.1' value on the Parameter Window. With both histograms perfectly seated,
you will obtain the best possible tonal values in your image when you decode the
wave file.
Use the To allow for this, some adjustments must be made to the PLL and AFC fields in
the parameter
window. Make sure that the 'Lock' option is checked, as usual, then
reduce the PLL value to 0.85. With a good quality tape deck this adjustment
alone should straighten your images, but if not, further reductions may be
tried. I have successfully used 0.5 to decode some old Okean-2 tapes. Generally,
the AFC field need not be changed, though increasing the value may be helpful in
difficult cases.
If decoding continues to produce slanted images, there are two more
adjustments that are possible. Because of the deficiencies of both tape-deck and
sound-card, it may be that the effective subcarrier frequency entering wxsat
from the sound-card is not precisely 2400 Hz. Decode part of the image, then
check under the First, select the "NO_VIS+IR" parameter set from the
This time, the entire histogram from the start of the black curve, to the
conclusion of the red curve, must sit squarely between zero and 1.00 on the
horizontal axis.
The lower histogram consists of two overlapping curves, the black channel-2
trace and a multicoloured trace representing channel-4. First, adjust 'Ampl.1'
to fit the black curve between zero and 1.00 on the horizontal axis ( exactly
the same as last time ), then adjust 'Ampl.2' to make the coloured curve
straddle the same range. Now decode a NOAA wave file, and look particularly at
the colour of the land. If the land is too blue, the coloured histogram must be
slid along its axis in a leftwards direction using the 'Offset 2' option.
I find that the default value of -0.12 has to be decreased to between -0.20
and -0.30 to produce land showing pleasing green and brownish tones. Experiment
till you find the value that seems most realistic, then note down the new
parameters so that they can be edited into the wxsat.dat file for future use.
Provided output from the receiver into the sound-card is constant, these
settings should not require changing again.
This acts on a completed image. Click on this menu to convert the
mouse-cursor into a vertical line. Next, move this cursor over the completed
image to that part that should be lined up with the left-hand side of the
monitor screen, and click the left mouse-button. Almost instantly, the image
will be correctly aligned and may now be saved in this form.
The second item in the
This is what happens if the input level from the receiver exceeds the a.g.c.
thresh-hold, the image being marred by the appearance of triangular wedges
produced as the a.g.c. attenuates the peak white in the image margin.
The solution to this problem lies in careful adjustment of an external
potentiometer, as mentioned earlier. This may be used to attenuate the signal
entering the soundcard so that its peak value falls below the a.g.c.
thresh-hold.
I have found the utility invaluable for automatically capturing a series of
passes from a variety of weather satellites by the simple expedient of setting
my receiver in scan mode, with the squelch operative. Whenever a signal opens
the squelch, the transmission is saved as a WAV file. This overcomes the
inability of WXSAT to interface with the receiver, and allows me to capture NOAA
12, NOAA 14 and Meteor signals during the same day while I am out at work. All
these signals may subsequently be displayed using WXSAT.
RECALL is available in both 16-bit and 32-bit versions from
http://www.sagebrush.com/
Processing Wave Files
With the WAV file temp.wav safely stored on your
hard drive, you now possess an accurate representation of the original audio
signal from the NOAA satellite, and this may be decoded time and again while you
experiment with the variables in wxsat's Parameter
Window. To do this, open the Optimising Image Quality
Earlier, I indicated that you should have
checked the GenCalibVar box in the Parameter Window
before decoding an image. When this option is set, wxsat generates calibration
data during image construction. This has the effect that, at the end of
satellite reception, the Adjusting Peak Value
Selecting wxsat's 
Setting wxsat's amplification parameters
At this stage your images may
well appear satisfactory, but further improvements in brightness and contrast
are almost certainly possible. The 
Saving Default Parameter Sets
Once the parameter set which produces the
best image from your WAV file has been established, it should work well for any
future images acquired from the same satellite. It is sensible to make a note of
these settings, then edit them into the WXSAT.DAT file within the application
directory. This may be accomplished using any suitable text editor ( Windows
Notepad or Write are ideal ). Next time you load wxsat, these will load as the
default settings for that satellite. Note that while the various parameters may
be altered on-screen, these changes are temporary, and are not retained by the
program for future decoding sessions. Permanent changes must be edited into the
wxsat.dat file by the use of a text editor.
Automatic Image Acquisition
For those of you who have to be at work for
most of the day, automatic, unattended reception of satellite images is highly
desirable, and wxsat is well able to meet this need through the Decoding Taped Images with WXSat
I know that many weather satellite
enthusiasts find that r/f interference from the computer degrades satellite
images, and take the precaution of recording on tape while the computer is
switched off, then decoding later. This method is particularly helpful when
dealing with horizon-grazing passes, which are most vulnerable to this effect.
To decode from tape, you have to make some minor adjustments to your default
parameter set. Because of unavoidable irregularities in the speed of a tape
drive, recorded images will usually decode slanted using the default wxsat
parameters.
Colour Composite Images
Wxsat can produce attractive coloured images by
using the IR channel data to impose a colour palette on the visible image. This
simple process does produce surprisingly attractive results once you have
optimised the parameters, in particular, detailing layering in cloud structure
by subtle changes in hue. Only the middle luminance values are modified by this
process, as WXSat retains black and dark neutral shades for the lowest
intensities ( sea ) and white and light greys for the highest intensities (
cloud ). Alas, the manual provided with wxsat really makes a very poor job of
explaining how to produce consistently high quality colour images. Here's how to
set about it.
Single Channel Coloured Images
It is also possible to apply colour to
single channel images from any satellite, though quality is less satisfying than
in the dual channel method. However, it is the only way of colouring Meteor,
Okean and Meteosat images. To do this, select Meteor or whatever, and check the
'Color' box ( but not the DualCh box ! ), and proceed as above. The upper
histogram reverts to a single black curve, but there are again both a black and
a coloured curve on the lower histogram. The coloured curve provides a fixed
range of colours which are applied to the image being decoded. As before, use
'Offset 2' to slide this colour palette across the intensity histogram to
produce the most pleasing effect.
Image Editing
Wxsat is by no means over-endowed with image editing
features ( load images into your paint program for this ), but the two it
possesses can be very useful indeed. Sometimes, particularly with satellites
such as Okean and Sich which have no distinctive toneburst to signal the start
of each image line, the image may well be displayed with its edges in the centre
of the screen ( as if it had been slid sideways, and wrapped round the screen ).
Wxsat can rectify this through its Summary
Wxsat must rate as the best entry-level software available for
decoding weather satellite signals, particularly as the author offers it free
for amateur use. In addition to producing monochrome APT images showing striking
detail, the program boasts a host of features for optimising image quality, many
not mentioned in this article. For the enthusiast who enjoys experimenting,
wxsat is a dream come true. In addition to decoding transmissions from the polar
orbiting satellites, wxsat also deals effectively with transmissions from
Meteosat ( though not to the extent of operating capture schedules or creating
animations ), and there is a mode for decoding HF WEFAX
APPENDIX A
Using WXSAT in 8-bit decoding mode
It was recommended earlier that the
16-bit audio setting on wxsat's Parameter Window
be checked for image acquisition. But what if you are using an older 8-bit
soundcard ? Most soundcards operate an automatic gain control ( a.g.c.) in 8-bit
mode, a feature that can weak havoc with your images.
APPENDIX B
RECALL
Recall is a utility that produces WAV files, and though it has no
facility to produce images, its WAV files can subsequently be decoded by wxsat.
RECALL was originally designed to respond to speech fed into a soundcard via a
microphone. The idea was that only the dictated speech should be recorded, and
lengthy pauses in the audio stream would automatically be ignored. It later
became apparent that the same principle made the program admirably suited for
the automatic capture of APT satellite transmissions and HF-FAX.