Servet,

Just to clarify a few items. On Friday in an email to the HLUG, I said:

> From my reading of the code, there is no way for you to put in the
> diffuse and direct components without changing it. The code needs to
> be edited in order to do that. The simplest approach is probably:
> 1) Make your input irradiance file have two additional columns, one
> for diffuse and one for direct irradiance
> 2) Edit irradat.f to correctly read, store , and return this information
> 3) Edit incfiles.for to not call gcirrad

Note that the above steps do not perform a compilation. They merely
consist of editing files.

Really, I need to add a few steps:
First, you should really completely read the Hydrolight 4.2 Technical
Documentation (h42techdoc.pdf, in the Documents folder), especially
portions of Appendix A (especially "Other Troubleshooting" and "General
Information") and Appendix D.1.

4) At this point, you need to compile the files to make an executable.
This may be done as described in the Hydrolight Technical Manual - see
Appendix A "General Information" section. What you need to do is to open
a windows command prompt (or dos command prompt) window. Change drives
to the drive where the Hydrolight directory lives on. Change directories
to the Hydrolight's maincode directory. Follow the compilation
instructions given in Appendix A. This creates an executable known as
maincode.exe.

Then change to the Hydrolight run directory. Then you need to issue the
following command:
..\maincode\maincode.exe  <  .\batch\Iroot.txt
but instead of "Iroot.txt" use the name of the input file that you want
to use, which usually exists in the HL's run\batch folder.

Good luck,

-M

Servet Ahmet Cizmeli wrote:

>I understand it much better now, especially after Marcos' comments.
>
>Thanks Marcos, thanks Lydia.
>
>One more question: Looking at my newly compiled incfiles.for, I see that
>the routine GCIRRAD is still being called to estimate the diffuse and
>direct components of Edtot (which is now read off disk from my data
>file). Is there a way to incorporate into H42 our spectral measurements
>of eddir and eddif? The only option I see in the GUI is the parameter
>"cloud" which is a scalar between [0-1] and does not fully account for
>the spectral shape of the components.
>
>
>
>Yahoo! Groups Links
>
>
>
>
>
>
>

--
Marcos Montes, Ph.D.
Research Physicist
Code 7232, Naval Research Laboratory, Washington, DC 20375
marcos.montes@... \W: 202-767-7308 \ Fax: 202-404-5689

I understand it much better now, especially after Marcos' comments.

Thanks Marcos, thanks Lydia.

One more question: Looking at my newly compiled incfiles.for, I see that
the routine GCIRRAD is still being called to estimate the diffuse and
direct components of Edtot (which is now read off disk from my data
file). Is there a way to incorporate into H42 our spectral measurements
of eddir and eddif? The only option I see in the GUI is the parameter
"cloud" which is a scalar between [0-1] and does not fully account for
the spectral shape of the components.

Servet,

Ah, good, you found incfiles.for. When I wrote the email, I had
forgotten the incfiles.for is the actual one that gets compiled. There
is also a copy in the batch folder.

  From my reading of the code, there is no way for you to put in the
diffuse and direct components without changing it. The code needs to be
edited in order to do that. The simplest approach is probably:
1) Make your input irradiance file have two additional columns, one for
diffuse and one for direct irradiance
2) Edit irradat.f to correctly read, store , and return this information
3) Edit incfiles.for to not call gcirrad

-M


Servet Ahmet Cizmeli wrote:

>I understand it much better now, especially after Marcos' comments.
>
>Thanks Marcos, thanks Lydia.
>
>One more question: Looking at my newly compiled incfiles.for, I see that
>the routine GCIRRAD is still being called to estimate the diffuse and
>direct components of Edtot (which is now read off disk from my data
>file). Is there a way to incorporate into H42 our spectral measurements
>of eddir and eddif? The only option I see in the GUI is the parameter
>"cloud" which is a scalar between [0-1] and does not fully account for
>the spectral shape of the components.
>
>
>
>Yahoo! Groups Links
>
>
>
>
>
>
>

--
Marcos Montes, Ph.D.
Research Physicist
Code 7232, Naval Research Laboratory, Washington, DC 20375
marcos.montes@... \W: 202-767-7308 \ Fax: 202-404-5689

I understand it much better now, especially after Marcos' comments.

Thanks Marcos, thanks Lydia.

One more question: Looking at my newly compiled incfiles.for, I see that
the routine GCIRRAD is still being called to estimate the diffuse and
direct components of Edtot (which is now read off disk from my data
file). Is there a way to incorporate into H42 our spectral measurements
of eddir and eddif? The only option I see in the GUI is the parameter
"cloud" which is a scalar between [0-1] and does not fully account for
the spectral shape of the components.

Folks,

Marcos is correct that modifying runs outside of the UI is a task
that requires a lot of courage and should not be done cavalierly.

I also wanted to add that when we [finally] ,release v.5 of the code
(HE5, a free upgrade to all H42 users), the code will need to
recompile only very RARELY, in cases where the user has written their
own subroutine(s).   All input parameters will be stored solely in
the IROOT.TXT file and the vast majority of runs can be made using a
standard, pre-compiled (or compile once, if dimens.inc is changed or
you port to a different OS) code.  We did this to (1) make the
Iroot.txt files 'stand-alone' so runs can be repeated later, and (2)
to make it easier for users to call HE5 recursively from other apps
(though since it is not a DLL will still require some work on said
user's side).  Of course, this required some changes to the IROOT.TXT
format.

Other improvements include better ozone cllimatology (based on the
TOMS v8), the ability to run either Hydrolight or Ecolight (screaming
fast, azimuthally-averaged version), extending data files farther
into the near IR and UV, and surface files that account for the
change in index of refraction with wavelength.

Anyway, just a glimpse into the (hopefully very near) future!

Regards,
Lydia

Hi everybody,
I would like to use the spectral downwelling irradiance measurements
we performed above water surface instead of the Radtran sky model.
With the GUI (H42), I created two runs:
1. a run that uses the option RADTRAN
2. a second run that is exactly similar to the first one except that
it uses the option "USER-SUPPLIED DATA FILE" (E:\H42\data\irradata.txt)
When I compare the two Input files associated with these two runs, I
see that they are exactly the same (except the first-two lines). To my understanding, the two runs should create output files that
would exactly be the same... However in the output files, Ed above
surface are slightly different...
Am I missing something here? What is the parameter in the Input file
that makes Hydrolight use the sky model we want and to what RECORD
GROUP it does belong? I need to perfectly understand how it works as I
am building an automated system that will bypass the GUI and modify
the Input file for each run.
thanks from advance for your input
best
servet
My Input file:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
irrad
irrad
0 1 2 1 0 2 4 1 440 0.1 0.014 3 440 0.1 0.014 -2 440 1 0.014 3 440 0 1 ..\data\pfh2oab.txt
..\data\defaults\apstarchl.txt
dummyastar.txt
..\data\defaults\apstarchl.txt
0 -999 -999 -999 -999 -999 1 -999 -999 -999 -999 -999 bstarDummy.txt
dummybstar.txt
0 0 0 0.0005 0 0 0 0.0005 pureh2o.dpf
avgpart.dpf
27 405, 415, 427, 440, 450, 460, 470, 485, 495, 505, 515, 525, 535, 545, 560, 570, 580, 590, 600, 615, 625, 635, 645, 660, 670, 680, 685, 700, 0, 1, 0, 0, 4
2, 3, 30, 0, 0
0.00
0, 0
0, 11, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ..\data\pfh2oab.txt
1
E:\H42\data\a_phystar_2001_085.txt
dummyFilteredAc9.txt
dummyHscat.txt
E:\H42\data\CHL_2001_085.txt
dummyCDOMdata.txt
dummyR.bot
dummydata.txt
dummyComp.txt
E:\H42\data\irradata.txt
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-- Marcos Montes, Ph.D.
Research Physicist
Code 7232, Naval Research Laboratory, Washington, DC 20375
marcos.montes@... \W: 202-767-7308 \ Fax: 202-404-5689

Hi everybody,

I would like to use the spectral downwelling irradiance measurements
we performed above water surface instead of the Radtran sky model.
With the GUI (H42), I created two runs:

1. a run that uses the option RADTRAN
2. a second run that is exactly similar to the first one except that
it uses the option "USER-SUPPLIED DATA FILE" (E:\H42\data\irradata.txt)

When I compare the two Input files associated with these two runs, I
see that they are exactly the same (except the first-two lines).

To my understanding, the two runs should create output files that
would exactly be the same... However in the output files, Ed above
surface are slightly different...

Am I missing something here? What is the parameter in the Input file
that makes Hydrolight use the sky model we want and to what RECORD
GROUP it does belong? I need to perfectly understand how it works as I
am building an automated system that will bypass the GUI and modify
the Input file for each run.

thanks from advance for your input
best
servet

My Input file:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
irrad
irrad
  0             1             2             1             0
  2             4
  1             440           0.1           0.014
  3             440           0.1           0.014
-2             440           1             0.014
  3             440           0             1
..\data\pfh2oab.txt
..\data\defaults\apstarchl.txt
dummyastar.txt
..\data\defaults\apstarchl.txt
  0            -999          -999          -999          -999
-999
  1            -999          -999          -999          -999
-999
bstarDummy.txt
dummybstar.txt
  0             0             0             0.0005
  0             0             0             0.0005
pureh2o.dpf
avgpart.dpf
  27
405, 415, 427, 440, 450, 460, 470, 485, 495, 505,
515, 525, 535, 545, 560, 570, 580, 590, 600, 615,
625, 635, 645, 660, 670, 680, 685, 700,
0, 1, 0, 0, 4
2, 3, 30, 0, 0
0.00
0, 0
0, 11, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
10,
..\data\pfh2oab.txt
1
E:\H42\data\a_phystar_2001_085.txt
dummyFilteredAc9.txt
dummyHscat.txt
E:\H42\data\CHL_2001_085.txt
dummyCDOMdata.txt
dummyR.bot
dummydata.txt
dummyComp.txt
E:\H42\data\irradata.txt

Correct.  Thus a direction of theta = 45 deg, phi = 90 deg, is the same
direction either above or below the surface.  The theta,phi coordinate
system does not change depending on where you are.  If you're in the air
(depth flagged as -1) looking down in a given (theta,phi) direction,
then you're seeing the total upwelling radiance (in air) in that
direction.  If you're in the water looking in the same downward
direction, you're seeing the upwelling (underwater) radiance in that
direction.

Refraction at the surface is accounted for by the fact that radiance
from one quad in the air maps into one (or more) different quads underwater.

Curt

cindyzju wrote:

>
> So in the full radiance output file, if the radiance is just below
> the water surface (like say 0), the angle in that radiance table
> (theda and phi) should be referring to under water angle while the
> angle for the above surface (like say -1) radiance should be in the
> air. Am I right?
>
> Thanks
> --- In HydroLightUsers@yahoogroups.com
> <mailto:HydroLightUsers%40yahoogroups.com>, Curtis Mobley
> <curtis.mobley@...> wrote:
> >
> > The directions in H are defined by the partitioning of all
> directions
> > into "quads", as shown in Fig 2 of the Users Guide, and as
> described in
> > section 2.4 of the Users Guide. These directions/quads are the
> same
> > above and below the sea surface. Thus, for example, if the sun is
> in a
> > particular quad above the surface, its refracted beam will be in a
> > different quad below the surface (for a level surface). Let me
> know if
> > this doesn't answer your question.
> >
> > Curt
> >
> > cindyzju wrote:
> >
> > >
> > > If I use the full radiance output setting, the angle I get is
> below
> > > the water or in the air or depends on the which depth I am
> gettting
> > > from?
> > >
> > > thanks
> > >
> > >
> >
> >
> > --
> > -----------------------------------
> > Curtis D. Mobley, Ph.D.
> > Vice President and Senior Scientist
> > Sequoia Scientific, Inc.
> > 2700 Richards Road, Suite 107
> > Bellevue, WA 98005
> > voice: 425-641-0944 ext 109
> > fax: 425-643-0595
> > email: curtis.mobley@...
> > WWW: www.sequoiasci.com
> > personal: www.curtismobley.com
> > -----------------------------------
> >
>
>


--
-----------------------------------
Curtis D. Mobley, Ph.D.
Vice President and Senior Scientist
Sequoia Scientific, Inc.
2700 Richards Road, Suite 107
Bellevue, WA  98005
voice: 425-641-0944 ext 109
fax:   425-643-0595
email: curtis.mobley@...
WWW:   www.sequoiasci.com
personal: www.curtismobley.com
-----------------------------------

So in the full radiance output file, if the radiance is just below
the water surface (like say 0), the angle in that radiance table
(theda and phi) should be referring to under water angle while the
angle for the above surface (like say -1) radiance should be in the
air. Am I right?

Thanks
--- In HydroLightUsers@yahoogroups.com, Curtis Mobley
<curtis.mobley@...> wrote:
>
> The directions in H are defined by the partitioning of all
directions
> into "quads", as shown in Fig 2 of the Users Guide, and as
described in
> section 2.4 of the Users Guide.  These directions/quads are the
same
> above and below the sea surface.  Thus, for example, if the sun is
in a
> particular quad above the surface, its refracted beam will be in a
> different quad below the surface (for a level surface).  Let me
know if
> this doesn't answer your question.
>
> Curt
>
> cindyzju wrote:
>
> >
> > If I use the full radiance output setting, the angle I get is
below
> > the water or in the air or depends on the which depth I am
gettting
> > from?
> >
> > thanks
> >
> >
>
>
> --
> -----------------------------------
> Curtis D. Mobley, Ph.D.
> Vice President and Senior Scientist
> Sequoia Scientific, Inc.
> 2700 Richards Road, Suite 107
> Bellevue, WA  98005
> voice: 425-641-0944 ext 109
> fax:   425-643-0595
> email: curtis.mobley@...
> WWW:   www.sequoiasci.com
> personal: www.curtismobley.com
> -----------------------------------
>

The directions in H are defined by the partitioning of all directions
into "quads", as shown in Fig 2 of the Users Guide, and as described in
section 2.4 of the Users Guide.  These directions/quads are the same
above and below the sea surface.  Thus, for example, if the sun is in a
particular quad above the surface, its refracted beam will be in a
different quad below the surface (for a level surface).  Let me know if
this doesn't answer your question.

Curt

cindyzju wrote:

>
> If I use the full radiance output setting, the angle I get is below
> the water or in the air or depends on the which depth I am gettting
> from?
>
> thanks
>
>


--
-----------------------------------
Curtis D. Mobley, Ph.D.
Vice President and Senior Scientist
Sequoia Scientific, Inc.
2700 Richards Road, Suite 107
Bellevue, WA  98005
voice: 425-641-0944 ext 109
fax:   425-643-0595
email: curtis.mobley@...
WWW:   www.sequoiasci.com
personal: www.curtismobley.com
-----------------------------------

If I use the full radiance output setting, the angle I get is below
the water or in the air or depends on the which depth I am gettting
from?


thanks

I have one for the Mroot file.

Servet

Has anyone written a MATLAB routine to read the Droot.txt file
containing all the output of a standard run?

I have added a HydroLight Technical Note HTN5_Color.pdf discussing the
conversion of spectra to CIE (x,y,Y) and RGB values.  The current H4.3
version outputs CIE (x,y,Y) values as described here.  If you need
this and your version doesn't have the new code, let me know and I'll
send you the routines.

Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the HydroLightUsers
group.

   File        : /HTN5_Color.pdf
   Uploaded by : hydrolightman <curtis.mobley@...>
   Description : Converting Spectra to Color

You can access this file at the URL:
http://groups.yahoo.com/group/HydroLightUsers/files/HTN5_Color.pdf

To learn more about file sharing for your group, please visit:
http://help.yahoo.com/help/us/groups/files

Regards,

hydrolightman <curtis.mobley@...>

Hi everyone,

I've submitted a file at that describes a faster version of the
selpfbb subroutine. This subroutine is mostly used when there are
measured values of a, b, and bb. In this case, the new version of the
subroutine provides much faster calculations than versions provided
with Hydrolight. This is important because accurate calculations need
a fairly small value for the tolerance in bb/b at the ABACBB screen of
the user interface.

The improvement in the speed of the calculations and the results of
the calculations will vary depending on the IOPs, the physical
specifications (how deep, how many wavelengths, etc.) as well as
depending on the particular version of Hydrolight that you use. This
subroutine has been tested with a few different revisions of
Hydrolight 4.2 (an early version of Hydrolight 4.2, as well as the
with the latest revision). I have not yet tested it with Hydolight
4.1, some versions of which also have the selpfbb.f subroutine. I'd be
interested in hearing from anyone who has Hydrolight 4.1 about how
well it works.

The pdf file describing the subroutine is in the "Files" section  at:
http://groups.yahoo.com/group/HydroLightUsers/files/selpfbb_faster_MJM.pdf

The new subroutine is also in the "Files" section, and is at:
http://groups.yahoo.com/group/HydroLightUsers/files/selpfbb.f

-Marcos Montes
--

Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the HydroLightUsers
group.

   File        : /selpfbb_faster_MJM.pdf
   Uploaded by : mmontes <marcos.montes@...>
   Description : A faster selpfbb subroutine when using measured bb/b to
determine the phase function

You can access this file at the URL:
http://groups.yahoo.com/group/HydroLightUsers/files/selpfbb_faster_MJM.pdf

To learn more about file sharing for your group, please visit:
http://help.yahoo.com/help/us/groups/files

Regards,

mmontes <marcos.montes@...>

Using the same IOP value as input with homogeneous and infinite deep water body assumption, the maximum output depth is set 1m for one run and 5m for another run. The output reflectance is the same when chlorophyll fluorescence is not included in the calculation. However if chlorophyll fluorescence is considered in each run, the output reflectance is significantly different in the fluorescence region. The resulted fluorescence with 5m output depth is much larger than that of 1m. Anybody can tell me what is the reason for that?
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-- Marcos Montes, Ph.D.
Code 7232, Naval Research Laboratory, Washington, DC 20375
marcos.montes@...
W: 202-767-7308, Fax: 202-404-5689

Using the same IOP value as input with homogeneous and infinite deep
water body assumption, the maximum output depth is set 1m for one run
and 5m for another run. The output reflectance is the same when
chlorophyll fluorescence is not included in the calculation. However if
chlorophyll fluorescence is considered in each run, the output
reflectance is significantly different in the fluorescence region. The
resulted fluorescence with 5m output depth is much larger than that of
1m. Anybody can tell me what is the reason for that?

Allow me to answer...

When you choose the Petzold average particle phase function (named
"avgpart.dpf") in the pull-down memu, that phase function is used at
every wavelength and depth for scattering by particles.

When you choose a particular backscatter fraction (bb/b value), then H
generates a Fournier-Forand (not Petzold) phase function having that
bb/b value at every wavelength and depth (generated as described in
Mobley et al, 2002, Phase function effects on oceanic light fields, Appl
Optics 41(6), 1035-1050).

The only way to have H use different phase functions for different
depths and/or wavelengths is to input a file of, say, ac9 data with
b(z,lambda) and a file of, say, HydroScat 6 data with bb(z,lambda).
Then H will used the bb(z,lambda)/b(z,lamba) ratio to determine a
Fournier-Forand phase function with a different backscatter fraction at
each depth and wavelength.  When spectral b and bb data are inputted, H
linearly interpolates in depth and wavelength to get values at depths
and wavelengths not in the data sets.  For depths/wavelengths outside
the range covered by the data, H uses the values at the nearest
depth/wavelength.  E.g., if your b and bb data starts at 410 nm, but the
H run starts at 400 nm, H will use the IOPs at 410 for the wavelength at
400.  Thus H interpolates within data ranges but it does not extrapolate
outside the data range.

Let me know if this doesn't answer your question.

Curt

sa.cizmeli wrote:

> Hello everybody,
>
> I would like to have more details about the way Hydrolight extrapolates
> the Petzold bb at other wavelengths than that of Petzold's measurements.
> I am using our ac-9 measurements as input into the Hydrolight and
> playing with the backscattering fraction that is used in the choice of
> the VSF.
>
> I looked throught the documentation but I don't seem to find anything
> about it.
>
> thanks from advance
> servet
>
>


--
-----------------------------------
Curtis D. Mobley, Ph.D.
Vice President and Senior Scientist
Sequoia Scientific, Inc.
2700 Richards Road, Suite 107
Bellevue, WA  98005
voice: 425-641-0944 ext 109
fax:   425-643-0595
email: curtis.mobley@...
WWW:   www.sequoiasci.com
personal: www.curtismobley.com
-----------------------------------

Hello everybody,

I would like to have more details about the way Hydrolight extrapolates
the Petzold bb at other wavelengths than that of Petzold's measurements.
I am using our ac-9 measurements as input into the Hydrolight and
playing with the backscattering fraction that is used in the choice of
the VSF.

I looked throught the documentation but I don't seem to find anything
about it.

thanks from advance
servet

Hi everyone,

In the next weeks I am going to (try to) compile the main original
Hydrolight fortran code under linux/unix.
Among people using the version 4.2 of Hydrolight, is there anyone who
uses it under unix/linux?
I would be thankfull for advices and warnings. (I am all set for the
input files. I wrote a C program who generate my input files.)
Is there some more appropriate compilers and/or compiling options?
Is someone aware of libraries helping when compiling "windows" code
under linux/unix?
Is there some particular tricks to replace or modify specific windows
fortran files?

Sorry for the disturbance,

aymeric

Greetings,

Marcos Montes and Joe Rhea at the Naval Research Lab-DC have put
together a nice tech note on selection of output depths when
fluorescence or Raman scattering are included in a HydroLight run.
Bottom line: you need to pick a fine enough depth grid that linear
interpolation of the scalar irradiance Eo is a good approximation to
the actual Eo(z) profile.  Their note is posted as file
Inelastic_Depths_MJM.pdf.

Now that I'm aware of this requirement, I'll fix the code in version
5.0 to automatically save Eo on a high resolution depth grid,
regardless of the user-requested output depths.  Meanwhile, take heed
of Marcos's and Joe's warning on depth selection for runs including
inelastic scattering.

Many thanks to Marcos and Joe for this analysis and writeup,

Curt

I too would be very interested in trying out an interface on unix.
servet


--- Curtis Mobley <curtis.mobley@...> wrote:

> HydroLighteans,
>
> A new H user has just asked me if anyone has developed a
> frontend (in IDL, for example) that would allow him to run
> H under UNIX without going througt the Windows GUI.  Does
> anyone have such an interface for version 4.2?
>
> Cheers, Curt
>
> BTW, more stuff coming soon.
>
>
>
>




__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around
http://mail.yahoo.com

HydroLighteans,

A new H user has just asked me if anyone has developed a
frontend (in IDL, for example) that would allow him to run
H under UNIX without going througt the Windows GUI.  Does
anyone have such an interface for version 4.2?

Cheers, Curt

BTW, more stuff coming soon.

Hello again,

In response to a user's question, I have posted a note about the rho
values defined in my 1999 Applied Optics paper on the determination of
Rrs from above-surface radiance measurements (AO, 38(36), pages
7442-7455).  I have also posted a table of rho values as a function of
wind speed, sun angle, and viewing direction.

In response to another question, I have posted a note about the
fundamental limitations of radiance as a descriptor of light.

Enjoy, and keep those questions coming,

Curt

Hello HydroLight users,

Marcos Montes and Joe Rhea of the U.S. Naval Research Lab recently
noted that the solar azimuthal angle computed by HydroLight when you
enter the date, time, and location is incorrect.  This does NOT affect
HydroLight's computations, since only the zenith angle (which is
correct) is used to determine the sky radiance.  (Indeed, the sun's
azimuthal angle is set to zero by H after it is computed within the
RADTRAN subroutine "sunang".)  However, the incorrect azimuthal angle
is in the printout and therefore should be correct, even if it is not
used in computations.

To correct this bug:

1) go to file qasky.f in the maincode directory
2) go to subroutine sunang in that file
3) replace (or comment out) these four lines of code:

       sintmp = sin(abs(rha))*cos(rsdec)/sin(rsunz)
       rsuna = asin(sintmp)
       if(ylat .gt. sdec) rsuna = 180.0 / rad - rsuna
       if(xha .gt. 0.) rsuna = 360.0/rad - rsuna

with these three lines of code:

       sna=cos(rsdec)*sin(rha)
       csa=sin(rlat)*cos(rha)*cos(rsdec)-sin(rsdec)*cos(rlat)
       rsuna=(atan2(sna,csa)+4.0*atan(1.0))

The computed sun azimuth angle will then be correct.

As a test case, if you use (in the H GUI)
   day=164
   GMT=12.0
   longitude=-80.100
   latitude=26.020

the printout should show
    sun zenith angle =  71.57 deg
    sun azimuth angle = 72.60 deg

(The old, incorrect azimuth was 107.40 deg.)

Many thanks to Joe and Marcos for finding this bug and for giving me
code that works.  This is what I had in mind when I set up this users'
forum.

Cheers,

Curt

Hello HydroLight users,

I have posted five pdf files on the Yahoo site.  These discuss various
topics that may be of interest:  improvements to the RADTRAN
atmospheric model, effect of angular resolution in HydroLight, how H
models surface waves, energy conservation in H, and computation of
Secchi depths in H.

I have recently written code to compute the Secchi depth.  This will
be a standard output in the next version of H.  If you have immediate
need for Secchi depths, let me know and I'll send you H version 4.2
including the new Secchi routines (which run in H4.2, but I'm not sure
about older versions).

Cheers,

Curt Mobley

Hello HydroLight users,

My apologies for not being more active with this users' group, but I
have all of the usual excuses of overwork and laziness.

As you may know, my book Light and Water is out of print.  However, it
is now available as a searchable pdf file (with the errors of the
hardcover edition corrected) thanks to Steve Ackleson at the U.S.
Office of Naval Research.  I can send it to you as a CD (no cost), or
you can download it (22 Mbyte zip file) from my personal website at
www.curtismobley.com/LightandWater.zip.  Eric Rehm at the University
of Washington created the zip file (many thanks!), which also can be
downloaded from his Yahoo OceanOptics users' group site.  Send Eric an
email at eric@... if you would like to join the OceanOptics group,
which is very worthwhile.

To maximize your download pleasure, go first to www.curtismobley.com
and explore my web site, which has photos, trip reports, book reviews,
and acidic politcal commentary.  The "Curt's Work" page has a link to
the Light and Water download.

More soon, I hope!!

Curt