CORRIGE TUTORIAL

# Index {#index .Titles01}

Introduction. ..................................... 3

1\. What is CORRIGE? ..................................... 3

2\. How to obtain CORRIGE. ..................................... 3

3\. Running CORRIGE for the first time.
..................................... 4

3.1. Information needed to use CORRIGE.
..................................... 4

3.2. Format of the INPUT FILE. ..................................... 5

3.2.1. Name of the file. ..................................... 6

3.2.2. Header: File Identifier. ..................................... 6

3.2.3. Header: Labels. ..................................... 6

3.2.4. Data. ..................................... 7

3.3 Format of the OUTPUT FILES. ..................................... 7

3.4 Using the program. ..................................... 8

3.4.1. Gathering the program and files in the same folder.
................ 8

3.4.2. Starting CORRIGE. ..................................... 9

3.4.3. Parts of the screen. ..................................... 10

3.4.3.1. The Sounding Section. ..................................... 10

3.4.3.2. The Commands. ..................................... 11

3.4.3.3. The Zoom Section. ..................................... 13

3.4.4. How to interpret wind barbs.
..................................... 14

3.4.5. Flipping screens. ..................................... 15

3.4.6. Navigating along the sounding.
..................................... 15

3.4.7. Commands used to correct the data.
..................................... 15

3.4.8. Saving the corrections. ..................................... 16

3.4.9. Exiting the program. ..................................... 16

4\. Errors and how to correct them.
..................................... 17

4.1. Importance of knowing all sorts of possible errors.
...................................... 17

4.2. Observational errors. ..................................... 17

4.2.1. Angle read off by one degree.
..................................... 17

4.2.2. Scale in reversed order. ..................................... 18

4.2.3. Balloon passing through the center of the sky. ................
18

4.3 Processing errors. ...............\...................... 19

4.3.1. Ten degree errors. ..................................... 19

4.4 Error detection with CORRIGE. .....................................
19

4.4.1. Using the angles to detect errors.
...............\....................... 20

4.4.2. Using the wind profile to detect errors.
...............\....................... 22

4.4.3. Evident errors using CORRIGE.
...............\....................... 23

4.4.4. Subtle errors. ...............\....................... 24

4.5 Examples ..................................... 25

4.5.1. Obvious errors. ...............\....................... 25

4.5.2. Balloon crossing the north.
...............\....................... 35

5\. Problems and solutions. ..................................... 40

5.1. The program is not showing the data when I open the file
............... 40

5.2. I cannot load the data to work with.
..................................... 40

5.3. I need to go back to the WINDOWS mode without exiting
............... 40

6\. Quick CORRIGE summary. ..................................... 40

# Introduction {#introduction .Titles01}

The purpose of this tutorial is to present all the aspects related to
the use of the program CORRIGE to process pilot balloon observations.
This program will allow the user to convert angles captured with a
meteorological theodolite into wind information. CORRIGE was first
developed by Jose Luis Carrasco currently a member of the Mexican
Weather Service. The motivation was to process the pilot balloon data
that resulted from the EMVER 93 Experiment held in Mexico. After some
years, the program was subject to some modifications and the most recent
version was written by Doug Kennedy from the National Severe Storms
Laboratory (NSSL) of the National Oceanic and Atmospheric Administration
(NOAA). The final version of CORRIGE was released in the late 1990's.

# 1. What is CORRIGE? {#what-is-corrige .Titles01}

CORRIGE is a small program made to convert pilot balloon angle data into
wind observations. It also allows the user to subjectively make
corrections to the data. When executed, the program displays a graphic
interface that can graph evolution of the elevation angle and azimuth
angle with time, and finally the wind profile. Allowing the user to zoom
in or zoom out in order to check for strange readings, CORRIGE helps the
user to depict the location and magnitude of the errors, and
furthermore, correct them.

# 2. How to obtain CORRIGE. {#how-to-obtain-corrige. .Titles01}

The program can be easily downloaded from the PACS-SONET website of the
National Severe Storms Laboratory (NSSL) through the following
addresses:

<http://www.nssl.noaa.gov/projects/pacs/salljex/archive/corrige/CPP2.EXE>

or

<http://www.nssl.noaa.gov/projects/pacs/web/html/computerprograms.html>

If you find any problems when carrying out this procedure you can
contact the following persons: Javier Murillo at
<javier.murillo@noaa.gov>, Michael W. Douglas at
<michael.douglas@noaa.gov>, John F. Mejia at <john.mejia@noaa.gov>,
Raquel K. Orozco at <raquel.orozco@noaa.gov> or Jose M. Galvez at
<jose.galvez@noaa.gov> in order to obtain the program.

# 3. Running CORRIGE for the first time. {#running-corrige-for-the-first-time. .Titles01}

If you are running CORRIGE for the first time you will need to know how
to use the program but also you will need to learn about the format of
the input and output files. This chapter covers in detail the input and
output of CORRIGE and how to use the program starting from scratch.

# 3.1 Information needed to use CORRIGE. {#information-needed-to-use-corrige. .Titles01}

To use CORRIGE you need to have three things available: An INPUT FILE
(1), information about the elevation of the site (2), and the estimated
ascent rate of the pilot balloon (3).

![](media/image1.jpeg){width="5.9944444444444445in"
height="1.4597222222222221in"}

Figure 1. Diagram illustrating CORRIGE's input and output.

The INPUT FILE contains information of the pilot balloon sounding in the
form of time, elevation and azimuth angle of the balloon as viewed
through the optical theodolite. The elevation of the site, and the
ascent rate are both estimated quantities. The elevation will be useful
only to transform the vertical axis of the wind profile from meters
above ground level (m AGL) into meters above sea level (m ASL). The
ascent rate, however, is essential for the calculations of the winds.
Even though this quantity may be slightly modified by eddies in the
lowest portion of the atmosphere, it will approximate to a constant.
This is an important assumption you should be aware of when dealing with
pilot balloon observations: The ascent rate is used as a constant.

Even though you may have been given the elevation and ascent rate
information along with the raw data files, we will now briefly discuss
the procedures followed to obtain them. The elevation can be found
either on a detailed map or averaging many GPS altitude readings on the
site. The ascent rate, however, is harder to obtain. You need to perform
numerous double theodolite tests, then select the good soundings, and
finally average them.

You can also run CORRIGE for many files without having to restart the
program each time. There is an option to modify the ascent rate or the
elevation of the site if needed. This may be necessary when some of the
soundings either need a different ascent rate or correspond to different
locations.

# 3.2 Format of the INPUT FILE. {#format-of-the-input-file. .Titles01}

The INPUT FILE is a plain text file (ASCII format), which contains a
header and then information regarding the time, elevation angle and
azimuth angle captured during the pilot balloon sounding. It can be
edited with any text editor, but if you use Windows, we recommend
Notepad. You can also export it from EXCEL as "text delimited by
tabulations". The name of the file must contain only 8 characters
because CORRIGE does not behave well with files with longer names.

![](media/image2.jpeg){width="3.1145833333333335in"
height="5.177083333333333in"}

Figure 2. An example of an INPUT FILE for corrige.

The header is contained in the first two rows of the file. The content
of the first row is the file identifier. It is quite flexible and is
used only as a reference in order to verify the place an time when the
observation was performed. The second row contains the labels
corresponding to the three columns of data, which start in the third
row. The first column contains the time in minutes, the second contains
the elevation angle of the balloon and the third one the azimuth angle.
The angles need to be expressed in decimal notation and using dots for
decimal places. CORRIGE does not accept sexagesimal notation (minutes
and seconds), and does not accept commas either.

Figure 2 is an example of an INPUT FILE for CORRIGE. Before passing to
the next section, we will analyze some details that can be observed in
this example file and may be useful to the users.

3.2.1. Name of the file.

The name of the file must have 8 characters, as we mentioned earlier.
The filename should include information of the date, time and ideally a
short identifier assigned to the site. In this example the name of the
site was not included. The format used was month, date, year and hour
(MMDDYYHH). The extension could be set as ".dat" or ".txt". Some format
examples are:

  -------------- --------------------------------------------------------
  Code           Description

  YYMMDDHH       Year (YY), month (MM), date (DD) and hour (HH). This is
                 a standard format, and contains complete information
                 about the date of the file. Notice that it is
                 recommended to place the largest time interval first
                 just to aid file organization. Year goes before month,
                 month before day, and day before hour. The only
                 significant restriction of this file is that it does not
                 contain the name of the site, so if it gets out of its
                 folder you may not know what site it belongs to. This is
                 why it is so important to locate the information of the
                 sounding in the first row of the file itself as we will
                 soon discuss in detail.

  SSMMDDHH       Coded name of the site (SS), month (MM), date (DD), and
                 hour (HH). This format is slightly more useful in the
                 sense that moving the file from its folder will still
                 tell information about the site. The only restriction
                 would be that you would not be able to process different
                 years at 1 time.

  SSSMMDDC       This is the PACS-SONET Network standard format. The
                 first three characters correspond to a code assigned for
                 each pibal station. The month and date come next.
                 Finally, the hour is also coded.
  -------------- --------------------------------------------------------

Table 1. Options to name the pilot balloon input files.

It is recommended to place the hour in UTC time units, however, all
these details are up to the user. This is why it is very important to
know your data and your archives in detail before processing them.

3.2.2. Header: File Identifier.

The purpose of the heading is to include as much reference information
in the sounding as possible, especially the information that could not
be included in the name of the file. All this information will be placed
in the first line. A recommended format is:

*"Name of the site, complete date and time, ascent rate, type of
balloon"*

Remember that this line can contain both numbers and letters (i.e.
numeric or alpha-numeric characters) therefore you can place any
information you want.

3.2.3. Header: Labels.

The labels are placed in the second row. As the data must be organized
in columns starting with time, elevation and azimuth, the labels should
follow the same order. The language, abbreviations or any of these
details do not matter. It is just as a reference.

3.2.4. Data.

The data must be stored in three columns starting with the time, then
the elevation angle and finally the azimuth angle. Whenever there is a
blank space in the dataset, you just have to leave it blank as CORRIGE
is designed to ignore this blank space. This can be viewed in the
example at times 5.5 and 7 seconds. Also keep in mind that all the data
that requires decimal places must be typed using a dot instead of a
comma, since CORRIGE ignores the decimals if a comma is used as a
separator.

# 3.3 Format of the OUTPUT FILE. {#format-of-the-output-file. .Titles01}

CORRIGE creates two output files. Both files are in text format and
therefore can be read by any text editor. Both files have the same name
as the INPUT file, but will differ in the extensions. One of them will
have extension "COR" and the other "WIN".

![](media/image3.jpeg){width="4.875in" height="4.84375in"}

Figure 3. Example of a WIN file.

The COR file has exactly the same format as the input file. The only
difference is that it contains the corrected version of the data. The
WIN contains all the wind information in at least two different forms.
An example can be found in figure 3.

The first column in the WIN file represents the time in seconds. The
second and third columns contain the height of the balloon in meters
above ground level (m AGL) and in meters above sea level (m ASL)
respectively. The fourth and fifth columns indicate the position of the
balloon in meters using as a reference point the origin. The sixth and
seventh columns contain the direction and magnitude of the wind
respectively. The direction is in degrees using the decimal system and
the magnitude is in meters per second. The last two columns contain the
zonal and meridional components both in meters per second. The WIN file
is the desired output of the program.

When you save the data using CORRIGE's "write" command, the output files
do not replace the input files so you end up with three output files per
sounding: The DAT, COR and WIN files. This is a useful feature as you
may sometimes want to know what corrections, if any, were applied to
your sounding file, if that were the case. Corrections using CORRIGE
will be thoroughly described in chapter 4.

# 3.4 Using the program. {#using-the-program. .Titles01}

The core question: How to use CORRIGE? The program consists in one
single and fairly small (170 KB) executable file named "CPP2.EXE". It
can be executed on any WINDOWS PC by clicking or double clicking on it.
As this file is very small, it is easy to obtain and move between
folders or devices, which is very convenient. The program does not run
on the Windows graphic environment. This is a relatively old program
that runs under the DOS operating system.

3.4.1 Gathering the program and the files in the same folder.

![](media/image4.jpeg){width="3.3333333333333335in"
height="3.0104166666666665in"}

Figure 4. Files and program CPP2.EXE must be in the same folder.

CORRIGE has to be in the same folder as the files you want to process.
Therefore, you can copy the "CPP2.EXE" file into the folder where your
input data is stored. You will find that it is easier to move or copy
the program into the folder where the files are instead of moving all
your files onto the program's folder.

3.4.2. Starting CORRIGE

To start the program you typically click or double click on the
"CPP2.EXE" object (list item, thumbnail, direct access, icon, etc.).
When you do this, the computer screen will turn black and display the
screen shown in figure 5. The first thing the program will ask is the
station elevation in meters above sea level (m ASL). You have to use the
"backspace" key to erase the default value and place the right elevation
for your site.

![](media/image5.jpeg){width="3.6458333333333335in"
height="2.7291666666666665in"}

Figure 5 . CORRIGE's environment as soon as you start running.

The program will first ask for the Station Elevation.

![](media/image6.jpeg){width="3.6458333333333335in"
height="2.7395833333333335in"}

Figure 6. The second step is introducing the rise rate or ascent rate of
the balloon.

After doing this you press ENTER and a new question will appear: The
ascent rate of the pilot balloon in meters per second (see figure 6).
You should proceed the same way: Use the "backspace" key to erase the
default value given and enter the ascent rate. Hit ENTER. After
answering these two questions you will be inside the program and ready
to start loading your files. Figure 7 illustrates this but note that
from now on we will invert the colors of CORRIGE's screen in order to
help you save ink if you decide to print this document.

![](media/image7.jpeg){width="4.6875in" height="3.6875in"}

Figure 7. Empty screen ready for you to start working with the files.

3.4.3. Parts of the screen.

The program offers three divverenf views or screen modes: A mode to
display the elevation angle, another to display the azimuth angle and a
final one to display the wind profile. In the three views, however, the
screen layout remains the same.

The screen is divided in three parts. The largest part named as
"Sounding Section" in this tutorial, corresponds to the graphic of the
entire sounding. This section covers about 70% of the screen and is the
big box located to the left of the two small boxes. The smallest two
sections appear on the right hand side of the screen. The upper-right
section, which will be addressed as the "Command Section", contains the
list of commands available for the operation of the program. Finally,
the lower-right box, the "Zoom Section", is a window that zooms in the
sounding.

3.4.3.1. Sounding Section.

The entire sounding is displayed on the Sounding Section. The first two
modes will show the angles and the third mode the wind profile. When the
angles are displayed, the x-axis shows the time and the y-axis the angle
in degrees. When the wind profile is displayed the x-axis disappears and
the y-axis remains but now it shows the heights in m AGL. A description
can be found in figure 9.

![](media/image8.jpeg){width="4.6875in" height="3.6875in"}

Figure 8. Parts of the screen.

![](media/image9.jpeg){width="5.364583333333333in"
height="2.1041666666666665in"}

Figure 9. Sounding section screen modes.

3.4.3.2. The Commands.

The command section will always appear in the right-upper side of the
screen regardless of the graphic view. It serves just as a reference and
reminder. The commands are simple letters and signs located in the
keyboard and you can execute them just by pressing them. The windows
contain all the commands needed to use CORRIGE. Table 2 shows a detailed
list of the commands.

  ---------------- ------------------------------------------------------
  Letter "L"       Opens a dialog box to load the files.

  Letter "W"       Opens a dialog box to write the files.

  Right arrow      Advances one position. It moves the cursor towards the
                   right when you are in the angle screen and moves it up
                   when you are in the wind profile screen.

  Left arrow       Retreats one position. It moves the cursor left when
                   you are in the angle screen and moves it down when you
                   are in the wind profile screen.

  Letter "R"       Resets the changes whenever you made any corrections.

  Arrow Up         Corrects the data adding one degree to the angle's
                   current value.

  Arrow Down       Corrects the data subtracting one degree to the
                   angle's current value.

  Letter "C"       Corrects the data making a linear interpolation and
                   using neighboring observations. Not recommended.
                   Should be used as least as possible.

  Letter "T"       Probably the most used, switches graphic views of
                   CORRIGE. Goes from the azimuth angle screen onto the
                   elevation angle screen, into the wind profile screen
                   and back into the azimuth angle screen.

  Numbers 1-9      Allow you to switch along different vertical
                   resolutions on the zoom window.

  Letter "S"       Opens a dialog box to modify the ascent rate.

  Letter "E"       Opens a dialog box to modify the station elevation.

  Escape           Opens a dialog box to quit the program.
  ---------------- ------------------------------------------------------

Table 2. Commands.

The most used commands will be the right and left arrows to navigate
through the sounding; the up and down arrows to correct errors by adding
or subtracting one degree; the command "T" to flip between different
screen modes (angles or wind profile); the command "L" to load files and
the command "W" to write files. The command "ESC" will also be needed to
exit the program. The rest of the commands are not used with the same
frequency but are useful and sometimes necessary.

3.4.3.3. The Zoom-in Section.

The axes in the zoom-in section do not have labels, however, they will
be the same as the ones in the sounding screen. Whenever CORRIGE is in
angle mode, this window gives the user the option to modify the vertical
resolution of the scale in to ease the detection of errors. You can do
this by pressing any numbers from one to nine. Number one will change
the vertical resolution to one degree per mark (the default) resulting
on the largest vertical resolution. Number nine, in contrast, results on
the lowest vertical resolution displaying nine degrees per mark. Figure
10 shows an example of an error (look for the discontinuity on the
curve) in which the use of the higher resolution becomes critical to
detect it. Use lower resolutions whenever the slope of the curve is too
steep to show several points in the zoom-in window. After reading this
tutorial you will learn that to detect errors you must revise at least a
couple of neighboring observations to the left and also to the right of
the error.

![](media/image10.jpeg){width="3.5833333333333335in" height="2.625in"}

Figure 10. Zoom section.

The zoom section, as mentioned priorly, does the same function when
changing into the wind profile mode. In this window, however, both the
horizontal and vertical scales of the zoom remain fixed. This zoom,
though, will always be good enough as to show you the vertical structure
of a section of the profile composed by 9 levels, as indicates the
example used as figure 11.

The zoom window in the wind profile screen displays information about
wind profile using wind barbs. It also includes information of the wind
velocity in knots to the left of the barbs, and the elevation above sea
level to the right of the sounding wind barbs. This will aid the user to
get accurate data instead of having to estimate it using the barbs.

The wind barbs are graphed in knots and following the north hemisphere
format which implies that for an easterly flow the velocity barb should
be underneath the direction barb. This does not affect the data, it is
just a convention.

![](media/image11.jpeg){width="5.208333333333333in"
height="4.083333333333333in"}

Figure 11. Zoom section in the wind profile window.

3.4.4. How to interpret wind barbs.

A wind barb is a symbol that transmits information about the wind
velocity and wind direction in an easy way. It was designed to ease the
interpretation of weather maps and now it is very useful when analyzing
vertical wind profiles as well. The tip of the barb, which sometimes is
a circle, indicates the location of the station or the place where the
wind is being measured.

The long line that departs from the circle represents the wind
direction. A barb that departs towards the north (up) indicates that the
wind is coming from the north. A barb that departs towards the east
(right) indicates a wind coming from the east, and so on.

![](media/image12.jpeg){width="5.208333333333333in"
height="1.1041666666666667in"}

Figure 12. Zoom section in the wind profile window.

The small line that departs from the long one indicates the wind speed.
A short line indicates 5 knots and a long line 10 knots. A triangle
indicates 50 knots. Whenever this line is absent the wind is between 0
and 2 knots. When there is no wind even the long line disappears and a
secondary circle is drawn around the station circle. Figure 12 displays
some examples regarding this topic.

3.4.5. Flipping screens.

As soon as we load a file, the azimuth angle profile screen APPEARS. In
the graphic, the x-axis is the time in minutes and the y-axis is the
angle in degrees. To flip into the elevation angle profile screen you
only need to press the letter "T" on the keyboard. To further flip into
the wind profile screen you need to do it again. Pressing "T" for the
third time will lead you back to the azimuth angle screen. Flipping the
screens is necessary to correct the data. See figure 13.

![](media/image13.jpeg){width="5.53125in" height="2.8958333333333335in"}

Figure 13. Flipping screens.

3.4.6. Navigating along the sounding.

To navigate along the sounding you need the right and left arrows. These
keys allow you to advance or retreat in the angle windows and to go up
or down in the wind profile windows. This is necessary because you often
want to zoom in a specific part of the sounding, so you need to position
the cursor in the section of interest. This is also essential as many
soundings need at least minor corrections and you need to place the
cursor in every value that needs to be corrected, as will be described
in the next section.

3.4.7. Commands used to correct the data.

Whenever you identified an error that can be corrected using CORRIGE,
which will be treated in the next chapter, you have to first place the
cursor over the observation and then correct it. To place the cursor
over the observation you can navigate using the left and right arrows.
After you do this you can correct the data by hitting the up or down
arrows, which will add or subtract an amount of 1 degree per hit.

![](media/image14.jpeg){width="4.9375in" height="2.625in"}

Figure 14. Example of how to correct the data.

Another method to correct the data is using the command "C", which
performs a linear interpolation using the surrounding observations. This
second method is not recommended unless it becomes really necessary.
Most of the errors can be corrected using the first method, especially
considering that most of them will be integer number differences.

3.4.8. Writing the new data.

To write the corrected data you only need to press the letter "W" on the
keyboard. Inmediately the program will ask you the question "Filename to
savir" and displaying the name of the file you just opened. You are free
to press ENTER because CORRIGE will not erase or modify your input file.
It will only create the two output files which have the same name but
different extensions: COR and WIN. If you regret saving the data you can
press "Esc" and the window will close without saving your data.

3.4.9. Exiting CORRIGE.

CORRIGE can be exited using the command "Escape" or "Esc" located in the
left and upper part of the keyboard. Whenever you press the program will
ask you the question "You wanna salir?" and to exit you just need to
press the letter "y" that corresponds to "yes". By pressing "n" the
program brings you back to the screen you were working on.

# 4. Errors and how to correct them. {#errors-and-how-to-correct-them. .Titles01}

Chapter 4 will cover the subject of errors that occur during pilot
balloon observations. We will review the importance of knowing the types
of errors, then go through observational and processing errors, then
about how to detect the errors using CORRIGE and then how to correct
specific errors. Finally we will go through some examples that may help
you understand the process of correcting errors with CORRIGE.

# 4.1 Importance of knowing all sorts of possible errors. {#importance-of-knowing-all-sorts-of-possible-errors. .Titles01}

The process of gathering research data is a long one, unfortunately, and
it is exposed to different sources of error. Whenever the dataset is
finally archived in a computer the quality may have been reduced by a
large sum of errors of different kinds. To make the best out of the
dataset you will need to clean it by going through quality control
procedures. To do this it will be therefore important to know all
sources of error, understand which ones can be corrected, learn how to
correct them, and furthermore, correct them.

# 4.2 Observational errors {#observational-errors .Titles01}

This is the broadest group of possible errors that may take place during
the process of gathering pilot balloon data. They occur during the
process of observation. Observational errors tend to be related mainly
to an bad reading mistaken by the observer, but also due to other causes
such as a lost of adjustment in the optical theodolite, a lack of
precision, and mistaken setting of the equipment. This section of the
tutorial will discuss the most common types of observational errors
starting with the most frequent ones. Even though some examples will be
included, most of the examples will be presented in section 4.6 of this
tutorial.

4.2.1. Angle read off by 1°

This is probably the most frequent error found in pilot balloon
observations. It occurs when the observer reads an angle higher or lower
than the correct one in 1°. It will tend to happen particularly when the
decimals lay between \~.8 and .0, especially if the calibrated drum is
not well aligned (it should read exactly zero when the mark on the
azimuth scale corresponds exactly with a degree graduation on this
scale). The observer may get confused when reading the decimals, and
commit a 1 degree error. This error will be obvious within CORRIGE and
can be easily corrected. An example can be observed in figure 15.

![](media/image15.jpeg){width="3.5104166666666665in"
height="1.8020833333333333in"}

Figure 15. Angle read off by 1°.

4.2.2. Scale read in reversed order

This error is also common among observers with little experience and it
is produced when the observer gets confused with the direction of the
scales. This error typically produces readings, which are off by 2°, 4°,
6°, 8°, etc. Sometimes the error can be as high as 18°, but this is does
not occur very often.

The confusion occurs because of two facts. The first one is that the
elevation angle scale increases towards the right (as any conventional
scale in the western hemisphere), whereas the azimuth angle scale
increases towards the left, this is, rolls in inverse order. A second
fact is that sometimes when the observer reads the angle scale, he/she
may find many small degree marks surrounding a simple numerical value,
which makes it harder to read than other situations when two numerical
values are visible. This may confuse him/her, and since the readings
have to be carried out quickly, he/she might unwillingly reverse the
scale. Figure 16 illustrates a sounding with a 10 degree error, which
may have been caused by this problem.

Some illustrative examples include reading 41 instead of 39, 231.5
instead of 228.5 or 347 instead of 353. If you notice, the correct value
is a mirror of the error with respect to the closest product of 10.
Analyzing the same examples respectively, the closest product of 10°
will be 40° for the first case, 230° for the second case and 350° for
the last one. See figure 17.

4.2.3. Balloon passing through the center of the sky

This error can be common in some locations where persistent wind
circulations may cause the balloon to pass near the center of the sky,
this is, right above the theodolite. During the observation the proper
thing to do is to rotate the theodolite about 180° in order to avoid the
elevation angle to become larger than 90°, which would be unrealistic.
Sometimes when this situation occurs, however, the observer does not
have enough time to rotate the theodolite 180° and he/she may remain
following the balloon with the elevation angle higher than 90°. Figures
can be found in the example section.

CORRIGE does not accept elevation angles larger than 90°. Any values
larger than 90 degrees will be converted by the program to 90.0. If this
is the case the program will not plot the sounding correctly. CORRIGE
can not help with this type of error and one way to correct it involves
the use of a spread sheet or any other program as you need to modify
both the elevation and the azimuth angles using formulas.

The procedure to correct this error follows. First you need to depict
all the sector of the sounding that has elevation angles equal or larger
than 90°. Then you must apply the following equation to the elevation
angles:

  -----------------------------------------------------------------------
  Final elevation = 180° -- Actual elevation

  -----------------------------------------------------------------------

And the following equation to the corresponding azimuth angles:

  -----------------------------------------------------------------------
  New azimuth = 180° + Actual azimuth

  -----------------------------------------------------------------------

If the value of any new azimuth angle equals or exceeds 360° you must
apply only to those azimuth angles the following relationship:

  -----------------------------------------------------------------------
  Final azimuth = Actual Azimuth -- 360°

  -----------------------------------------------------------------------

When the file is corrected you should then run CORRIGE in order to
correct other possible errors.

# 4.3 Processing errors. {#processing-errors. .Titles01}

Processing errors occur when dictating or typing the data. They are less
common than the observational errors and all of them can be corrected
using CORRIGE, unlike the observational errors, which in some cases will
not be correctable using CORRIGE.

4.3.1. Ten degree errors

This is a fairly common error, but it is easy to correct within CORRIGE.
Mappens more frequently as a processing error but it can also occur as
an observation error. It basically happens when the person typing or
digitizing the data could not hear or read well or read well the tens of
the angle. The same applies to one, two or even three hundred degree
errors.

# 4.4 Finding errors with CORRIGE. {#finding-errors-with-corrige. .Titles01}

Input files you process with CORRIGE for the first time will most
probably contain both observing and processing errors. There are two
ways to start looking for errors with CORRIGE. One of them is to start
the detection using the angle curves and the other is start looking at
the wind profiles. It is easier to start with the angles and then get
some help from the wind profiles for reasons we will describe next. We
will also discuss in this section about some criteria proven useful to
correct the data.

4.4.1. Detecting errors using elevation and azimuth angle curves.

The easiest way to start depicting errors is using the elevation and
azimuth curves. We recommend, however, start using the wind profiles
instead as there are some criteria developed for this and the results
cab be more reliable. Most of the angle curves tend to be smooth, which
eases the detection of errors. Figure 16 is a clear example of this.
There is an obvious error in about minute 7 (see arrow), when the
azimuth angle profile jumps from a value of about 140° to an angle of
about 150° and back to 140°. This seems to be a 10° error. This type of
error is very easy to recognize even without zooming on it. In most
other cases zooming in on the error becomes necessary.

![](media/image16.jpeg){width="4.6875in" height="3.7395833333333335in"}

Figure 16. A 10-degree error example.

Many errors are smaller in magnitude and the zoom-in feature will be
very useful to depict them. It is the case of the one degree errors
which are relatively common. Sometimes, though, more than one one-degree
error may occur very close to each other and complicate things a little.
If this is the case, the recommendation is to use the wind profile as a
guidance to decide which observations are erroneous and which ones are
correct. A good sounding will produce a wind profile with smooth changes
in wind direction and speed. Also, values of vertical shear of \~50kt
per km or higher should be looked into as possible errors. Only in
regions where jets or other wind-related phenomena occur, sharp changes
in the wind profile may happen. If this is the case, though, the new
wind speed should be consistent in at least 3 observations. Abrupt
changes that occur in one observation and disappear in the next one can
be taken as errors.

Some legitimate situations in which the profile may appear too sharp are
the following. One common situation is when the balloon crosses the
north, this is, when the azimuth angle changes from 359° to 0°. The only
way for CORRIGE to graph this change is to generate a sharp jump in the
azimuth angle that at first seems to be an error. With practice you will
find out that this situation is not hard to solve. A 360° jump on the
screen will immediately tell you that the jump is justified as long as
the rest of the sounding is consistent with the jump. Figure 17
illustrates a situation when this occurred. In this example the jump is
a valid situation. Just visualize the first part of the sounding being
placed over the 360° mark and the sounding will become smooth.

![](media/image17.jpeg){width="4.6875in" height="3.7708333333333335in"}

Figure 17. The balloon crossing the north is reflected as a jump in
CORRIGE's azimuth angle profile.

Another realistic situation may cause the angle profiles to look sharp
is when the balloon crosses close to the center of the sky. When this
happens the elevation angle reaches a maximum, and the azimuth changes
very quickly sometimes veering or backing almost 180°. This will not
generate jumps as sharp as in the prior case but may generate large and
continuous changes in the azimuth angle accompanied by a maximum in the
elevation angle that must coincide with the sharpest change in the
azimuth. The characteristic signature of this case is that the elevation
angle must be high, generally higher than 70 degrees.

A final situation that may be misleading in CORRIGE is when there are
sharp wind direction and/or wind speed. These are frequently associated
to low-level jets, strong diurnal breezes opposed to the synoptic flow
and other particular situations as was mentioned before. The rule of
thumb is to check if the change is consistent along the sounding, this
is, if the wind speed is consistently higher (or lower) in at least
three consecutive levels (readings).

After gathering some practice you will be able to notice when abrupt
changes correspond to an error and when not.

4.4.2. Using the wind profile to detect the errors.

Once in a while you may be fooled by the angle profiles. This can happen
for example when an error occurs near a change in the slope of the curve
or when the elevation angle jumps from a value close to 360 to a value
close to zero or viceversa (i.e. the pilot balloon crosses through the
north). While the user may be thinking that the jump and the nearby
observations may be correct, sometimes there may be hidden errors that
are only visible in the wind profile screen. In other cases both the
elevation angle profile and the azimuth angle profile may appear smooth
enough as to be correct, however some errors may be present that may be
more visible when analyzing the wind profile. Even if you find yourself
more comfortable by starting with the angle profiles, you should always
go through the wind profile as it is the final output, and may show
features that the angle profiles will not.

In some situations it may be easier to identify an error through the
wind profile screen than through the angle screens. Some useful criteria
to identify errors in the wind profile have arisen from knowledge in
meteorology. Developing sharp deterministic criteria for the
identification of errors, though, is a hard task. Even when applying
established criteria, the correction of errors should always be
performed carefully. There are cases in which the errors are so small
that they become hard to depict, particularly when the scale of the
natural variability of the atmospheric flow has an order close to the
order of magnitude of the errors.

The criteria used to detect errors in the PACS-SONET pilot balloon data
were the following. An error is assumed to be present when either the
wind component "u" or "v" changes at a rate of 50 m/s in 1 km, or more.
Another criteria more applicable to CORRIGE is to check for possible
errors whenever there is a change of 5 knots in the wind speed between
one level and the next. An error will almost always exist when the
change of speed between two consecutive levels is in the order of 10
knots. It is recommended to use some guidance from the wind direction as
well. Strange changes in the wind direction may be related to errors.

![](media/image18.jpeg){width="2.5729166666666665in"
height="3.0729166666666665in"}

Figure 18. Evident errors in the wind profile.

Figure 18 shows some evident errors on the wind profile. In this case
the change is of 9 kt in 217 meters, then 15 kt in the next 216 meters,
then 21 kt in the next 217-meter layer and finally 14 kt from 7008 to
7225 m ASL. There are many indicators here that tell you that an error
is present. Firstly, there are too many abrupt changes in a very small
portion of the sounding. In fact, there is an abrupt change in every
level through four consecutive levels. Secondly, the magnitude of the
changes is in the order of 10 knots and sometimes even 20 knots. The
last indicator is that there is also a sharp change in the wind
direction. In this case there are probably two errors in the angle data
since one error in the angles creates two bad data points in the wind
profile. This is due to the particular design of the program and also
due to the fact that each angle value is used twice in determining the
horizontal displacement of the balloon.

Other criteria that should be considered is that large changes in wind
direction can occur, but only when the wind is very weak, this is, close
to calm. If you see that the wind direction in your profile is changing
significantly in a certain layer and that calls your attention, the
first thing you should check is the wind speed. If you find that winds
are weaker than 3 knots your data may be correct. If your wind speed,
though, is of about 5 kt or larger, you should definitely seek for
errors in the angle profiles.

4.4.3. Evident errors that cannot be corrected using CORRIGE.

There are some evident errors that cannot be corrected using CORRIGE.
Some of them are listed as follows.

1.  When the elevation angle is larger than 90 degrees. This errors
    shows up as a flat section in the angle curve in color yellow. This
    error, described priorly in this document, occurs when the balloon
    crosses the center of the sky and does not give enough time to the
    observer to turn the theodolite 180 degrees. The way to correct this
    error is by using a spread sheet or any other program that can apply
    the equations described in section 4.2.3.

> Elevation angles larger than 90 degrees can also occur when the
> elevation angle column is flipped with the azimuth angle column.
> Before continuing we should flip the order of the columns using a
> spread sheet or a text editor.

2.  When commas are used instead of dots, the angle curves take the
    shape of stairs. This happens because CORRIGE ignores the decimals
    and all the values are assumed to be integers. The solution is to
    change the commas for dots with a spread sheet or text editor before
    continuing with CORRIGE.

3.  Another error occurs when the azimuth angle is larger than 360
    degrees. CORRIGE does nor accept values equal or larger than 360
    degrees. If this occurs, the program obtains a fake value by
    interpolation of neighboring values. The new value will appear as a
    yellow dot. This error can be corrected using CORRIGE, but it is
    recommended to be corrected in the DAT file.

4.  In some occasions error in the time column might occur. In some
    soundings a value of "05" was digitized instead of a value of 0.5.
    Even though this error is very evident in CORRIGE it can not be
    corrected with the program . Few people detect this error and if
    they do they do not know how to correct it.

4.4.4. Subtle errors.

This section discusses the errors that are the hardest to detect. These
errors can not be corrected using CORRIGE but what is worse is that they
can not be detected using CORRIGE either. The most common errors are
described as follows.

1.  The most common error occurs when the heading has less than two
    lines. In this case CORRIGE does not read the first observation or
    the first two observations. In this case the time in the WIN file
    starts in minute 1.0 or 1.5.

2.  Another frequent error occurs when the time is digitized in
    sexagesimal format (mm:ss). This error can be easily identified by
    carefully observing the sounding section, not the zoom section. Most
    of the times this error will be almost undetectable. When this
    happens CORRIGE ignores the seconds and the WIN file results in
    values of 0.0, 1.0, 1.0, 2.0, 2.0, etc in the time column.

# 4.5. Examples. {#examples. .Titles01}

In this section we will present a short and very diverse set of examples
about how to correct some errors. Please notice that we will discuss the
correction of specific errors instead of going though the correction of
the entire profile.

4.5.1. Obvious errors.

Obvious errors can be considered to be the several types of degree
errors such as 1, 10, 100, 200 and 300 degree errors. These are easy to
detect with CORRIGE and also easy to correct.

The most common way to proceed is to detect obvious errors in the
azimuth angle curve and correct them. The same can be done using the
elevation angle curve. At a first glance errors are not obvious so we
use zoom-in window to find them. We notice the presence of an error
located near observation #7 (figure 19). It is a 1-degree error. Small
degree errors may not be obvious unless you use the zoom-in window to
detect them. As we are dealing with an obvious error we can correct it
and proceed to revise the elevation angle curve. To correct them we only
need to subtract 1 degree using the "down arrow" key. Figure 20 shows
the corrected angle.

![](media/image19.jpeg){width="5.395833333333333in"
height="4.197916666666667in"}

Figure 19. 1-degree error as displayed by the zoom-in window.

![](media/image20.jpeg){width="5.395833333333333in"
height="4.270833333333333in"}

Figure 20. The error in the azimuth angle profile is corrected using the
down arrow.

After correcting all the obvious errors in the azimuth angle curve we
proceed to the elevation angle curve. We find some obvious errors in
observations 7 and 8 as shown in the zoom window of figure 21.
Observation #7 needs to be added 1 degree and observation #8 needs to be
subtracted 1 degree.

![](media/image21.jpeg){width="5.4375in" height="4.270833333333333in"}

Figure 21. Errors in the elevation angle curves.

Figure 22 shows the elevation angle curve after the corrections. Figure
23 shows the wind profile before the corrections and figure 24 after the
corrections. When we complete the correction of all the obvious angles
we can start correcting the harder ones.

![](media/image22.jpeg){width="5.395833333333333in"
height="4.270833333333333in"}

Figure 22. Now we smooth the errors in the elevation angle profile.

#  {#section .Titles01}

![](media/image23.jpeg){width="5.395833333333333in"
height="4.270833333333333in"}

Figure 23. Wind profile. The cursor is placed in observation #7.

![](media/image24.jpeg){width="5.395833333333333in"
height="4.270833333333333in"}

Figure 24. This time the corrections result on minor changes in the wind
profile.

In this case the impact of the corrections have been small. The higher
the location of the errors the larger the impact they will have on the
sounding.

*Example 2: One degree error.*

Figure 25 shows a one degree error in the elevation wind profile. This
is another simple example. After loading the file we did not find any
suspicious observation on the azimuth angle profile, therefore, we
switched into the elevation angle profile. The way to correct this error
is to add 1 degree.

![](media/image25.jpeg){width="4.802083333333333in"
height="1.7291666666666667in"}

Figure 25. Elevation angle curve showing a 1-degree error.

![](media/image26.jpeg){width="5.395833333333333in"
height="1.8333333333333333in"}

Figure 26. Azimuth angle profile.

In this case the azimuth angle curve (figure 26) shows no obvious errors
in the observation that corresponds to the error in the elevation angle
curve. Figure 27 shows the wind profiles before and after the
correction. The impact of this one single correction is small but
noticeable. There is a change in direction and wind speed from a
northwesterly wind at 4 knots to a west-northwesterly at 7 knots.

![](media/image27.jpeg){width="5.479166666666667in"
height="4.354166666666667in"}

Figure 27. Wind profile before correction (A) and after correction (B).

*Example 3: Two degree error.*

Figure 28 shows a 11-degree error located at minute 23. It is an obvious
error and this one can be detected even without zooming-in on it.

![](media/image28.jpeg){width="4.5in" height="3.2291666666666665in"}

Figure 28. Azimuth angle screen.

Figure 29 shows the error as viewed in the zoom-in window using
different vertical resolutions. When large errors like this occur it may
be easier to use smaller vertical resolutions when zooming-in. In this
case the 2-degree per mark vertical resolutions better displays the
error.

![](media/image10.jpeg){width="3.5833333333333335in" height="2.625in"}

Figure 29. Playing with the vertical scale of the zoom screen.

The impact of this error is large and can be easily detected in the wind
profile. Figure 30 shows the elevation angle curve in the left panel and
the wind profile curve in the right panel. As you can see, there was no
obvious error in the elevation angle curve at the observation that
corresponds to the error in the azimuth angle curve. The large impact
can be attributed to the 11-degree error in the azimuth angle profile.

![](media/image29.jpeg){width="5.104166666666667in"
height="4.052083333333333in"}

Figure 30. Always revise elevation angle profile and the wind profile.

#  {#section-1 .Titles01}

#  {#section-2 .Titles01}

*Example 4: 100-degree error.*

This error is pretty obvious. In this case the observer(s) was(were)
distracted and committed the same error in two consecutive observations.
It is still an obvious error because the jump was of about 100°, a round
number, and after two observations the curve jumped again to follow the
initial curve's tendency. The error is even more obvious when analyzing
the wind profile. Figure 31 includes the azimuth angle curve, the
elevation angle curve and the wind profile. The elevation angle curve
was displayed to show that the errors in the wind profile were caused
solely by the errors in the azimuth angle profile.

![](media/image30.jpeg){width="5.833333333333333in"
height="4.166666666666667in"}

Figure 31. Effects of a 100° error.

Figure 32 shows the corrected errors in the azimuth angle curve and the
impact this has in the wind profile.

![](media/image31.jpeg){width="5.03125in" height="3.3645833333333335in"}

Figure 32. Correction of a 100° error.

*Example 5: Correcting all the obvious errors in an entire profile.*

This profile has several obvious errors which can be easily corrected.
Figure 33 shows the obvious errors in the elevation angle curve and in
the azimuth angle curve and their corrections.

![](media/image32.jpeg){width="5.447916666666667in"
height="2.8333333333333335in"}

Figure 33. Correction of several obvious errors.

Figure 34 illustrates the wind profile with errors and figure 35 the
same profile after the corrections.

![](media/image33.jpeg){width="1.5625in" height="3.125in"}

Figure 34. Wind profile after initial correction.

![](media/image34.jpeg){width="3.0208333333333335in"
height="3.0208333333333335in"}

Figure 35. Wind profile after all corrections.

4.5.2. Balloon crossing the north.

A peculiar situation occurs when the balloon crosses the north, as
described previously in this document. This results in a large jump from
values just below 360 degrees to values just above 0 degrees. This jump
may initially seem to be an obvious error but it is not. When the jump
takes place only once and the curves are smooth in both sides of it, the
jump will tend to be valid.

To make sure the jump is valid it is recommended to revise the elevation
angle curve and the wind profile. Figure 33 shows an example of a
correct sounding. There is large jump in the azimuth angle but both the
elevation angle and the wind profile look coherent. Figure 34 also shows
a good example of this situation.

![](media/image35.jpeg){width="5.104166666666667in" height="4.25in"}

Figure 36. Balloon crossing the north.

#  {#section-3 .Titles01}

![](media/image36.jpeg){width="4.833333333333333in"
height="3.7291666666666665in"}

Figure 37. Balloon crossing the north, another example.

*Example 2: Error close to valid jump.*

Figure 38 shows an azimuth angle curve. In this case the balloon has
crossed the north as suggested by the large jump from near zero to near
340 degrees. There is another jump, however, right after the 340-degree
observation. For people with not much practice it may seem hard to
detect where the error is, or how to correct it.

![](media/image37.jpeg){width="4.6875in" height="3.7083333333333335in"}

Figure 38. What is wrong in this azimuth angle curve?.

In this case it is recommended to seek guidance in the wind profile.
Before doing this, though, we check the elevation angle curve for
errors. Figure 39 shows this curve.

![](media/image38.jpeg){width="4.6875in" height="3.75in"}

Figure 39. Elevation angle seems fine.

In this case the elevation angle curve appeared to be correct, so any
clear errors in the wind profile will be related to the error in the
azimuth angle. Figure 40 shows the wind profile with a clear error near
3001 m ASL.

![](media/image39.jpeg){width="4.6875in" height="3.6458333333333335in"}

Figure 40. Initial wind profile.

If you have experience with CORRIGE, you will find that there is a
50-degree error in the observation right after the jump. If you are not
sure about the magnitude of the error, you can make an initial
correction and revise the results using the wind profile until the winds
are smooth in direction and speed. Figure 41 displays the corrections
done to this profile. The solution was to add 50 degrees into the 230
degree observation.

![](media/image40.jpeg){width="5.395833333333333in"
height="3.0729166666666665in"}

Figure 45. Profiles before and after the correction.

This is a good example of a situation in which utilizing the wind
profile may greatly ease the depiction of errors. You should always
revise the wind profile before making any corrections as some sharp
features in the angle profiles may be correct.

# 5. Problems and solutions. {#problems-and-solutions. .Titles01}

5.1. The program is not showing the data when I open the file.

1.  Check if the decimals are separated by dots or commas. They should
    be separated by dots.

2.  Check if the file is being opened by any other program such as
    EXCEL, NOTEPAD, or WORDPAD. Close the file if this is the case and
    rerun CORRIGE.

3.  Close the whole program that was opening the file and rerun CORRIGE
    again.

4.  Check you're opening the right file. Has the file you want been
    placed in the folder you are running CORRIGE? Or, has CORRIGE been
    moved to the folder where the files you want to process are?

5.2. I cannot load the data to work with it.

1.  Make sure all your files are in the same folder than the program
    CPP2.EXE before you start running it.

2.  Check if the file is being used by any other program. If it is not,
    try closing all the other programs and rerun CPP2.EXE.

3.  Edit one of your data files using NOTEPAD and try to save it that
    way. Then rerun the program

4.  Make sure your files have 8 characters.

5.3. I need to go back to the WINDOWS mode without exiting.

1.  Press the keys "Alt" and "Esc" at the same time and CORRIGE will
    become another window in the taskbar.

# 6. Quick CORRIGE summary. {#quick-corrige-summary. .Titles01}

1.  Download the CPP2.EXE program through the following address:

> <http://www.nssl.noaa.gov/projects/pacs/salljex/archive/corrige/CPP2.EXE>

2.  Locate this program in the same folder where your input files are.

3.  Double click the icon, object file or direct access.

4.  Type the altitude of your site.

5.  Type the ascent rate used for your sounding.

6.  Load a file using the letter "L", selecting the file and then
    pressing ENTER.

7.  Switch screens using the command "T" and detect errors in the
    profiles, always seeking guidance through the wind profile, and
    using the zoom-in windows.

8.  Correct the errors by placing the cursor over the bad observation
    and adding or subtracting as many degrees as necessary with the up
    or down arrows respectively.

9.  Save the corrections using the command "W".

10. Exit the program by pressing "Esc".