LidarValidate1
==============

Keywords: lidar, validation

== Summary ==
This is a LIDAR verification/validation demonstration.  An Excel
spreadsheet is included which shows a hand-computed, "expected"
result which can be compared against the DIRSIG output.

== Details ==
The conditions for the validation case are summarized in the table below:

----
128        Number of pixel elements per side of array (e.g. 128 x 128)
1.064E-06  Wavelength [m]
1.500E-04  Pulse energy [J]
2.000E-09  Pulse length (rectangular/uniform pulse profile) [s]
1.000E+04  Pulse repetition rate (PRF) [Hz]
4.000E-01  Focal length [m]
0.10       Receiver radius [m]
8.000E-03  Beam divergence half angle @ 1s [radians]
5.000E-05  Size of pixel elements (lenslet size) [m]
0.10       Nominal target reflectivity (Lambertian assumption)
0.50       Optics throughput
2000.00    Range [m]
----

== Important Files ==
The parameters summarized previously are spread across the various input
files. The `demo.scene` file defines a flat plate scene with a 10%
reflectance.  The `demo.platform` file includes all the transmitter and
receiver parameters.  The `demo.ppd` file places the instrument the
appropriate distance from the scene.

=== Excel Calculation ===
The point of a validation is to compare the model output to an accepted
value.  In this case, an analytical computation was performed to produce
the accepted value.  This was accomplished in an Excel worksheet (see
`validate.xls`) that includes all the input parameters and then does a
step by step computation of the number of photons expected to arrive on
the focal plane.  

.Screenshot of the Excel worksheet to compute the expected value.
image::validate.xls.png[width=640]


== Setup ==
To run the simulation, perform the following steps:

. Run the DIRSIG `demo.sim` file

This produces the file `demo.bin`.


== Results ==
The expected value computed in the `validate.xls` file is *7.34537*.
This can be compared to the value output by the *BIN Analysis Tool*
when run on the `demo.bin` file, which is:

----
$ bin_analyze demo.bin
...
[header info deleted for documentation purposes]
...
Pulse #1:
    Minimum total photons in a pixel = 7.34517
    Maximum total photons in a pixel = 7.34517
    Pixels with zero total photons = 0/1 (0%)
    Average background photons per pixel = 1.09663e-05
    Average total photons per pixel = 7.34517

Complete!
----

