Copyright: Raymetrics S. A 2003-2004
Citation: Raymetrics S. A 2003-2004


Getting Started

General and Contact Information

Wellcome to Raymetric’s Lidar System software

Use this software for apparatus alignment, data acquisition and data preview and analysis.

For help on data preview and analysis refer to present help file

For help on data acquisition and alignment refer also to Licel’s manuals.

In this help file a theory chapter is also included

It is suggested to users to be familiar with Labview environment, although all the vi’s was programmed in such a way that users without prior experience in Labview could use them.

For information about Labview please refer to Labview User’s Manual

Contact Information:

raymetrics s.a

5 Kanari Str., Glyka Nera

15354 Athens, Greece

Tel: +302106041582

Fax:+302106041052

E-mail: support@raymetrics.gr


Getting Started Alignment and Data Acquisition

To start alignment or data acquisition alignment procedures

Go to Start  Programs  Raymetrics and click the “start” icon.

Choose one of the following actions.

1.	Coarse Alignment

2.	Fine Alignment

3.	Data Acquisition

Attention: Before call the interface is suggested to have already started triggering the system, and all cable connection have been done properly.

Only one action at a time is allowed

Move the cursor over the image to navigate to corresponding interfaces


Data Preview and Analysis

Using this program to preview old or new acquired data, to plot or to analyse (calculation of Lidar parameters) them.

A briefly description of the main actions following:

Use worksheet interface to insert data from external files or database into a worksheet.

Plot directly database data or from external files using Plot interface.

Create surface graphs from acquired data using Surface Graph Interface

Convert automatically database files to an ascii format to use them with other programs.

Open Data Preview and Analysis vi from program group raymetrics.

The window consists of a toolbar and the Main DB interface.

Move mouse over image to navigate.


Data Preview and Analysis - Graphics

Graphics

Two types of Graphs can be produces.

The called name 2D plot, which is a standard 2D plot Graph, and surface graphs.

Surface graphs contain data in time.


Data Preview and Analysis - Graphics - 2D Plots

2D Plots

The 2D Plot Interface (view image)

There are three main actions.

•	Import Data…

You can append data or to refresh the plot with newly inserted data. You can import data from an external data file or from the database interface.

•	Save As Ascii…

You can save an ascii files which contain ascii data. The first column are X-values data and the second is Y-values data. For multi-plots data are saved in the same file in the order of plotting.

•	Save Image.

Select a filename with jpg extension.

 If the file already exists will be overwritten without notification

At left side there is a list box containing the available plots. By selecting one (mouse left click) and clicking Del Plot button you can delete a plot from the graph.

You can also delete a point of a selected plot by moving the black cursor at the desired location and clicking Del Point Button.

Moreover you can delete a portion of a selected plot by moving the Red (initial point) and Blue (Final point) cursors to the desired locations and click the DarkBlue “OK” button.

To customise the appearance of the graph click on Edit Graph buttom


Data Preview and Analysis - Graphics - 2D Plots

EDIT 2D GRAPH

There are four Tabs.

•	Scale

•	General

•	Legend

•	Layout

Scale

Select a scale from the top Dropdown List.

Visible: Checked or Unchecked

Mode: Linear or Logarithmic

ScaleFit: 0-Do not autoscale, 1-Autoscale once now, 2-Autoscale

Font Color: Click on the color box to choose font’s color

Format and Precision block:

Format:Decimal (00.000), Scientific (00.E+x), Engineer

Precision: Number of Decimal Digits

Range block:

Minimum value of selected scale

Maximum value of selected scale

Increment (customize grid lines)

MajGridColor:

Click on colorbox to choose the color of gridlines for the selected scale. For invisible grids choose “T”

Label Text block:

Type into textbox the label for selected scale.

Choose the size, type and color

Move the blue mark at the right ramp to move the label across the selected scale

General Tab

Plot Area:Colors Cluster

Choose the background color of the graph and color for the axis from the corresponding colorboxes (BG Color, FG Color respectively)

Caption Cluster

Click on the white board while pressing shift key to move the caption to the desired location

Legend Tab

Customise Plot Name, Symbol Type (For no symbol choose “No” option) and Symbol Color, Line Type, Line Color and Plot Size (Line and Symbol)

Click on the white board while pressing shift key to move the Legend to the desired location

Layout Tab

Click on arrows to move and size the graph.

Preview at the white board

Black outlined rectangles: Scales

Blue filled rectangle: Caption

Red filled rectangle: Legend

Grey outlined rectangle: Whole Graph


Data Preview and Analysis - Graphics - Surface Plot

Surface Plot

View Surface Plot interface

At surface plot x-axis is time, y-axis is Height (altitude+binwidth *number of channels) in kilometers, and z-axis the selected parameter (Raw data, Slog, DSlog, RCS, A, B).

You can produce surface plots by inserting files from the database interface. Choose start time and stop time (they must belong on the same set of measurement) from the database interface. Choose the desired dataset and press ok. If you want to change timescale press cancel and start over.

If you have already insert data and you want to expand the timescale (x-axis) click again “Insert Files” button.  If the new timescale overlaps with the old one the surface plot is not refreshed. In case of time gaps, blank (zero data) strips are produced.

Be sure always to insert the same dataset otherwise unpredictable results can occur.

You can save surface plot as an image file (jpg format) by clicking on “Save as Image” button. By pressing “Save Ascii” button you can save data in ascii table-form data file.

Caution: if the timescale is long enough and you have also interpolate the plot then the resulting ascii file could be enormous. In that case please wait.

Clean plot by clicking “Clear Graph” button.

Interpolate data in timescale by setting the Interpolation value between 0 and 10.

Change the Height Limits of the plot by changing the first and the last value in Y-axis.

Caution:  Do Not change Timescale Limits manual.

Press “Lidar Calc” button to calculate Lidar parameters.


Data Preview and Analysis - Worksheet

WORKSHEET

View worksheet interface

To import external data or existing data from database view  click “Insert Data” button.

To change a value to a shell just click on it and type a new value.

You can delete a row or a column in two ways

a.	Select a column or a row and press the appropriate button at the right side of the interface.

Info: by choosing this method you can delete multiple rows or columns

b.	Or rightclick and select the appropriate command from the DropDown List.

Caution: 1. Keep the size of the worksheet short, otherwise a “memory full” message might appear with unpredictable results.

Caution: 2. When selecting multiple rows, do not exceed the number of visible rows.

To set the values of the first empty column press “Set Col Value” button.

Refer to columns as c1, c2 etc., and to index as i.

Simple functions are supported.

Example: c3=c1+sin(c2)*i

See Formula supported Function

To save worksheet as an ascii table formatted file press “Save as Ascii” button.

To calculate Lidar Parameters select a column and press “Lidar Calc.” button.


Lidar Parameters Calculation

STEP by STEP description

1.	Call the interface

2.	If more than one dataset have been imported select one.

3.	Set initial and final height of interest by moving the appropriate cursors (red Init Index, red Final Index) at the Raw Data Graph

4.	Set first and last channels for background calculation by moving the appropriate cursors (yellow Bround1 and yellow Bround2 respectively)

5.	Set the values to General Parameters Block

6.	Set the values to Rayleight Parameters Block

7.	Set the values to Filter Parameter Block

8.	Set the values to Klet Parameter Block to calculate A and B parameters


General Parameters

Init Index and Final Index: Select the Height Zone of interest (look at message board)

Bround1 and Bround2: Select the Height Zone where the background calculation takes place.

Resolution: binwidth length in kilometres

Altitude: Altitude of the apparatus in kilometers

Z. Angle: Zenith Angle

Overlap F. Cor: Overlap function correction

Tr. Delay F. Cor: Trigger Delay function correction

Dead T. F. Cor: Dead time function correction

Blue marked parameters are automatically set when the lidar calculation interface is called from database view or surface plot interfaces.


Rayleight Parameters

Wave L.: Detected wavelength in Armstrong units

(this parameter is automatically set when the lidar calculation interface is called from database view or surface plot interfaces)

Pressure: Ground Pressure in hPa units

Temper.: Ground Temperature in Celsius.

Min R.(Km): Minimum Rayleight reference height in kilometers

Max R.(Km): Max Rayleight reference height in kilometers

Blue marked parameters are automatically set when the lidar calculation interface is called from database view or surface plot interfaces.


Filter Parameters

Zone1: Move the yellow cursor, named Zone 1, of the Plot Parameter Graph

Zone1 is defined between Initial Height of interest and the position (Height) of zone1 cursor

Zone2: Move the yellow cursor, named Zone 2, of the Plot Parameter Graph

Zone2 is defined between position (Height) of Zone1 cursor and the position (Height) of cursor Zone2

Type of Filtering: Select type of filter (Zone Median, Zone Glidding)

N1: Number of channels to be used for filtering in Zone1

N2: Number of channels to be used for filtering in Zone2

N3: Number of channels to be used for filtering in Zone3

Zone 3 is defined between the position (Height) of Zone 2 cursor and the last height of interest.


Klet Parameters

K-ref (Km): Klet reference altitude in Kilometers

RFDISK: BackscatterRatio [BETA/BETA(Ray)] at Klet Reference altitude

Lidar Ratio: Lidar Ratio (1/C). Data Range between 10 and 50


Message Board


Data Preview and Analysis – DateBase View Interface

DataBase View Interface

View interface

This interface is a multi purposes. It is used for several tasks such as to convert multiple files to ascii format, to import data into a worksheet or into a plot graph and finally to import a timescale into a surface plot.

Depending on where it is invoked, several sub-interfaces appear.

The main interface is similar to Main DB window interface.

It is consisted of:

A Main Table, whose every record represent a set of measurement

A Filelistbox whose contents are the filenames which belong to the selected record of the Main Table

An Info Block which contain information and plots for a selected filename from the Filelistbox.

And two commands buttons: Set As Start and Set As Stop buttons. By using this two buttons a file name or many of them can be selected for further processing.

A Filter Block for filtering records into the Main Table.


Data Preview and Analysis – Database View Interface

Sub-Interfaces

There are three sub-interfaces.

1.	Sub interface for exporting data to a worksheet or a 2D Plot (preview)

a. Consist of a XY multi graph

b. All Data Set: check box for selecting all available dataset from the selected file or files,

c. a drop-down list for selecting a dataset if the All Data Set checkbox is not checked

d. Raw Data: check box for exporting raw data

e. SUM: check box for average calculation of the selected dataset (in case of multiple file selection).

f. check box for exporting one of the available Lidar parameters (in case of unchecked Raw Data check box)

g. INDEX as X: check box for exporting as X-values the number of channels instead of height.

h. Min Toggle Frequency: Min Toggle Frequency: Below this frequency the photon counting data is used only, since the tha analog data has worth SNR and the differential nonlinearity starts to influence the data.. Between max. and min.  toggle frequency it is assumed that both the analog and the photon counting are valid.

i. Max Toggle Frequency: Above this frequency the analog data is used, since the photon counting starts to be nonlinear. Between max. and min.  toggle frequency it is assumed that both the analog and the photon counting are valid.

2.	Sub interface for exporting data (timescale) to a surface graph (preview)

a.	a drop-down list for selecting one of the available datasets

b.	Type of interpolation controls the interpolation method applied to datasets (linear, polynomial, spline, rational)

c.	The number of points to be interpolated between two data points, not including the data points themselves

d.	Min Toggle Frequency: Below this frequency the photon counting data is used only, since the tha analog data has worth SNR and the differential nonlinearity starts to influence the data.. Between max. and min.  toggle frequency it is assumed that both the analog and the photon counting are valid.

e.	Max Toggle Frequency: Above this frequency the analog data is used, since the photon counting starts to be nonlinear. Between max. and min.  toggle frequency it is assumed that both the analog and the photon counting are valid.

3.	Sub interface for saving raw data of multiple files to as ascii files (preview).


Software Installation

Raymetric’s Lidar systems are supplied with a computer system which has already installed all the necessary software for apparatus alignment, data acquisition and data preview and analysis. The following instructions are given in case that a reinstallation of the software is needed.

Before install contents of the supplied CD make sure to install first Labview version 6.1 or higher.

When insert the supplied CD from raymetrics s.a. a setup program starts.

Setup program copies vi’s to selected installation folder and creates a program group called reaymetrics.

When installation is finished, run the configuration utility.

In case of failure copying, manually copy all the contents of vi folder of the supplied cd to a desired location.

Caution: For proper use of the supplied vi’s uncheck “Use localised decimal Point” option

Step by step procedure:

-Open Labview

-Select new vi

-Go to Tools menu

-Select options

-Go to front panel section

-Uncheck (if checked) “Use localised decimal Point” option


Software Installation

Configuration Utility

For running manually configuration utility just open <installation path\Registry Tools\Config Application.vi>
This is an autorun vi.

Select the type of Transient Recorder Tr-xx-yy

xx: Sample rate

20 MHz (7.5 range resolution)

40 MHz (3.75 range resolution)

yy: FIFO memory Lenth

160 (16384 databins)

80 (8192 databins)

Select default location (folder) for saving raw data during data acquisition

Select default location (folder) for ascii data when converting raw files to ascii format

Select default location (folder) for backup raw data.

Press Ok to confirm or cancel to quit.


Print

Depending on running interfaces three command buttons are activated or deactivated.

Write text to “Description” items to comment out images.

Set page merges by changing values of left, right, top and bottom items.

All printing jobs are send to the default printer of the system.


Main Database Interface

Main Database Interface is consisted of:

A Main Table, whose every record represent a set of measurements.

Each record has the following fields:

UserName: is the username that is entered when someone call data acquisition interface.

Location: Is the Location which is entered during global information configuration procedure.

Start, Stop Time and Date

Whenever a single measurement is saved, a new record is added to the main table with same start and stop date and time fields.

For multiple measurement start date and time fields shows the data and time information from the first filename of a set of measurements and stop date and time fields from the last saved file.

The owner of a record (a set of measurements) might delete it (all files contained to the selected record, will be also deleted) or edit it, by doubleclicking on a record.

A Filelistbox whose contents are the filenames which belong to the selected record of the Main Table

An Info Block which contain information and plots for a selected filename from the Filelistbox.

Upper left block contains trigger’s information.

Upper right block contains general information (which are set by configuring global information during measurement acquisition) of the set of measurements such as altitude, longitude etc.

Several rows below describe every dataset of the selected file. Select a raw to view corresponding plot.

Every raw consist of eleven shells.

Tr.: Transient recorder device

Wave L.: Detected wavelength

Polarization Type: p-parallel, s – cross, o – no polarization

Type: AN-analog, PC – photon counting

Scat. Type: scattering type, elastic (emitted wavelength equal to detected wavelength) anelastic (emitted wavelength not equal to detected wavelength)

Chan: Number of channels recorded

Res: resolution = 2 ^ (reduction number) * resolution (7.5 for Tr 40 or 3.75 for Tr20) in meters

Distance: maximum distance in meters

H. Volts: High voltage (V)

Shots: Number of shots

R/D: For analog: input range (mV), for photon counting discriminator level.

Two commands buttons: Backup and Restore buttons (available only to administrator).

Administrator can backup the main table and all corresponding files to pre-specified location (during configuration utility)

Or restore files and tables.

Every time administrator backup files a new entry is added to the listbox below.

Use restore utility to restore files for further analysis.

Load current: use this button to load the default table and files which are those how reside to the default raw directory (during configuration utility)


Administrative Tasks

Three major extra operations can be accomplish by the administrator

A) backup database

B) restore a database

c) administrating users

About tasks A and B refer to Main DB interface

Add, remove or edit user information using Admin Users program from raymetrics group

Or

Open and run from explorer the <installation path\Administrative Tools.llb>

The software is shipped with a default administrator password (Look at printed documentation)


Ascii Conversion

To convert multiple files to ascii format press the command multi ascii from Data Preview and Analysis interface.

Select files by using start and stop buttons from database view interface.

Select the dataset to be converted from the sub-interface and press ok button.

Description of Header Lines:

First Line:

Filename: RMyyMddhh.mms

RM: default prefix, yy: year, M: month in hexadecimal, dd: day of month, hh: 24-hour, mm: minutes, s: seconds/10

Second Line:

Location: String with 8 Letters

Start time: dd/mm/yyyy hh:mm:ss

Stop time: dd/mm/yyyy hh:mm:ss

Altitude: four digits (meters)

Longitude: four digits (including –sign). One digit for decimal grades

Latitude: four digits (including –sign). One digit for decimal grades

Zenith Angle: two digits in degrees

Temperature: four digits, one for decimal, in celsius

Pressure: four digits, one for decimal, in mhA

For description on remaining lines refer to licel documentation (tr_manual.pdf)


Data Acquisition

Data Acquisition Interface

Call data acquisition interface by pressing data acquisition button at start.vi

Use this interface for single data acquisition or for multiple measurements.

Insert user name and password to proceed. This information is inserted into the Main Database for every successfully saved measurement a user complied.

By filtering database record is easy to select all the measurements a user has done.

Before start a measurement all parameters have to be configured.

After configuration press start button to start a measurement.

The transient recorders, in which you have activated data sets, should now acquire data if a sufficient trigger signal is connected to the input. If the acquisition has been started successfully, the number of shots done in the multiple acquisitions group should start increasing.

Press stop button to stop data acquisition. The waveform graph will be refreshed and will display the dataset  that the user has specified.

Press save button to save acquired data to a unique file for further analysis. A new record into the database will be added with the same values into the start and stop time fields.

For multiple data acquisition press start button. After starting the acquisition, the text of the button changes to stop, which indicates that the series of multiple acquisitions can be stopped by pressing this button again.

By starting multiple acquisition, the software automatically  accumulates the specified (in the global configuration section) number of shots data, The shotnumber is the number of averaged acquisition cycles (number of laser pulses) and is increased by one for every trigger pulse that is received (max  value is 4095 due to ram limitation),  and then automatically write it to a file with a unique identifier whose naming convention is explained in the Ascii Conversion Topic.

Every succesfull set of multiple measurement is corresponding to a new record into the main database with start time field shows the time of the first saved file and stop time field the time of the last saved file.

During multiple acquisition, click on monitor button to view a surface graph of the currently acquired data files. To refresh the monitor graph press once again the button.

Caution: Exiting program without previously stop a running multiple acquisition, may cause unpredictable entries into the main database.

For information about using the waveform graph refer to Labview manual.


Data Acquisition

Configuration of the System

Before starting acquisitions, you should configure the default global information to correspond to geographical details of your location, so that this information can be included properly in the header of the data files. After that, you will set up the Transient Information which is specific to your data set.

Configure Global Parameters

Set global information like Location of the measurement site (8 characters length), longitude, latitude and altitude (in meters), ground temperature (in Celsius) and ground pressure (in mhA). Emitted wavelengths and frequency from laser sources (1 and 2) can be set.

Finally set the shotnumber for the multiple data acquisition. The number of shots should be set high enough so that data files are not written more quickly than every ten seconds (i.e. 100 shots at 10Hz, 200 shots at 20 Hz, etc...). This is due to a limitation of the naming convention. The maximum allowable value is 4094 due to transient recorder ram limitations.

Configure Transient Recorder

After selecting to configure datasets, the default transient information found in the file Acquis.ini is preloaded and the user is given the possibility of configuring the transient recorder information using the interface shown below

Configure each transient recorder by change the index number.

Activate the desired memory bank (A, B and Analog, photon).

Set the number of bins (strob number) to read out from the memory bank. The maximum number of bins is given by 16384/(2^data reduction). Set the data reduction which allows for binning. A data reduction level of 0, 1 and 2 corresponds to a height resolution of 7.5m, 15m, and 30m respectively. Each increasing in value reduces the height resolution by 1/2 and doubles the number of bins that are combined together to make a superbin. Thus the levels 0,1,2 correspond to 1 , 2, and 4 bins per data point respectively.

Set the discriminator level for the transient recorder. There are 64 discriminator levels (values 0-63) which correspond to either a range of 0-24mV without gain reduction or 0-96mV with gain reduction.

Set the range values of the transient recorder. Valid values are 0-20mV, 0-100mV and 0-500mV.

Set parameters which indicate the type of equipment that is used in channel. This information is stored as a header in the data files, so that the user (or whoever has to evaluate the data) can see what parameters were used to take the data. The fields are used for the Channel A and B descriptions, the detected laser wavelengths and the corresponding polarization, the filter number of central wavelength, the photomultiplier voltage, the photomultiplier number and the type of photomultiplier used. The information entered in these fields has no effect whatsoever upon the data acquisition. It is used purely to store information about the experimental setup in the data files.

The menu item file contains four sub-items that the user can choose from.
If you would like to edit an existing file, choose "Load transient information" and select a file. After doing this, the information including the file path as shown in point 8 will be updated to the new data that has been read from the file. After you have edited the data and are satisfied with the configuration, you can save the information by choosing "Save transient information as..." and either choose the same file name, which overwrites the old file, or give it a new name. If you have edited the data and have made a mistake, you can reload the original information by pressing Reset Information.

After finishing configuration of  the transient recorders, you can exit the configuration program by either pressing the Save and Exit button, if you would like to save the information to the actual file path as shown, or, alternatively, you can press Exit without Saving or choose File->Exit in the pull down menu, if you would like to exit without saving your changes. Please note that when you exit the program without saving, any unsaved data is lost! Thus if you have configured the data and wish to keep it, you need to either choose Save and Exit or choose File->Save transient information as... from the pull down menu before you exit the program. If you want the current transient recorder configuration to be used as the default transient recorder information, you must save this data as Acquis.ini in the directory where HS16-Acquis.llb is located.

If you have followed the steps above, your transient recorders should now be configured for use with HS16-Acquis.


Alignment

The lidar alignment is achieved in two steps. During the first step (coarse alignment), the far-range signal is monitored and the optical axes are fixed in a position where that signal is maximum. During the second step (fine alignment), the range-corrected lidar signal (RCS)

is compared to the range corrected exponentially attenuated Rayleigh backscattered coefficient

,

at a range interval, which is considered free of any aerosol loading (pure molecular atmosphere). The molecular backscatter and extinction coefficients ( [image] and [image], respectively) can be calculated either from a Standard Atmosphere (U.S.S.A 1976) or more accurately from available local radiosonde data. The advantages of this method are that it does not require any extra equipment; it can be performed on line during daytime or night-time measurements and is very accurate.

Figure below shows a typical lidar signal correctly aligned ‘matching’ the pure molecular atmosphere (fine alignment).

Lidar signal aligned ‘matching’ the pure molecular atmosphere.

Once the fine alignment procedure has been terminated the lidar system is ready to acquire elastic and inelastic lidar data.

To use coarse or fine alignment, run start.vi from raymetrics program group or directly from windows explorer or a shortcut. Click on the desired button to call the corresponding interface.

If the vi fails to run the interface is automatically closed.

Attention: Before call the interface is suggested to have already start triggering the system, and all cable connection have been done.


Alignment

Coarse Alignment

If all cable connections have been done and the system is triggered successfully, when open coarse alignment interface is running automatically and the shotnumber indicator increasing for every trigger pulse transient recorder receives (or a laser pulse if the recorder is triggered from the laser source).

 ShotNumber  indicator

Set the desired value for #update indicator.

When shotnumber is equal to update value the data are read from the recorder, are displayed at the graph and the procedure starts over until click exit button.

The dataset which is displayed to the graph depends on the selections you made.

Select devise, Mode and memory bank

Caution: During hardware installation make sure to connect the correct cables to the corresponding recorder unit at the Licel’s rack. Unit 0:532p, Unit 1:532s, Unit 2: 355, Unit 3: 387

Set Discriminator level, the number of bins to be transferred from the transient recorder and to be displayed (Strob Number) and the analog input Range of the preamplifier. The signal starts at 0 and extends to -20, -100, or -500mV.

Turned on the overflow swith, to display all bins with overflow as 0.

The small graph at the right corner of the interface shows the average of the region of interest on the waveform graph that is selected by using the cursors.The cursors at the right of the waveform graph allow for the selection of a region to average over. The average of the region selected is displayed in small graph at the right upper corner. The x and y controls at the left allow the user to allow for autoscaling of the x or y axis. Default is autoscaling for the y axis and fixed values for the x axis. These can be changed by sliding the controls. The x.xx and y.yy controls allow for the specification of the format precision and mapping modes of the x and y axis.

For further information refer to also to Licel’s documentation.

For more information about wavegraph refer to Labview manual.


Alignment

Fine Alignment

Before start fine alignment is recommended to have already starting triggering the system.

In the image below is displayed the interface of Fine Alignment.

The interface and the operation of the fine alignment interface is quit similar with Coarse Alignment interface.

Below deference’s are outlined.

Select height range for which the background calculation will be done be setting the first channel (1BC) and the length (2BC number of channels).

Height = 1BC* range resolution + altitude + range resolution/2)

Example: 1800*7.5 + 200 + 7.5/2 = 13.7 Km

Attention: Make sure that 1BC + 2 BC < ShotNumber

Set ground temperature and pressure of the measurement sites (in Celsius an mha respectively)

Set the height range interval, which is considered free of any aerosol loading (pure molecular atmosphere), by entering values to Min R and Max R parameters (in Kilometers)

Attention: Make sure that Max R < shotnumber*range resolution + altitude + range resolotution/2

Smooth acquired range corrected signal.

Smoothing is achieved by setting three height zones

First zone start from channel 0 and finish at Zone 1 Channel Index

Second zone start at Zone 1 Channel Index and stops at Zone 2 Channel Index

Third zone starts at Zone 2 Channel index and stops at channel equal to strob number

Attention: make sure that Zone 2 Channel index + N3 < strob number

In each zone a glidding filter is applied the corresponding N (N1, N2, N3)


External Data File

All ascii files which do not belong to the database system.

These files should contain valid table like data

View interface


Binwidth

Binwidth=Range Resolution * 2^(reduction number)

Range Resolution. For Tr20 Model is 7.5 meters and for Tr40 is 3.75 meters


Access this Help file


Indicators of running interfaces


U.S. Standard Atmosphere, NOAA, NASA, USAF, U.S. Government Printing Office, Washington D.C., 227, (1976).


The Memory A corresponds to acquisitions which were triggered by Trigger A, and the Memory B corresponds to acquisitions triggered at input B. If only one trigger input is connected to the trigger source, only one memory can hold data different from 0.


Strob Number

Indicates the number of bins (channels) of the selected transient recorder unit memory bank to read out.


The shotnumber is the number of averaged acquisition cycles (number of laser pulses) and is increased by one for every trigger pulse that is received (max  value is 4095 due to ram limitation)


the analog input range of the preamplifier. The signal starts at 0 and extends to -20, -100, or -500mV


Discriminator

Threshold levels of Discriminator for Photon Counting DataSets.

Values from 0 to 63


Start FrontPanel


Formula Supported Functions

Function		Description
abs(x)		Returns the absolute value of x.
acos(x)		Computes the inverse cosine of x in radians.
acosh(x)		Computes the inverse hyperbolic cosine of x.
asin(x)		Computes the inverse sine of x in radians.
asinh(x)		Computes the inverse hyperbolic sine of x.
atan(x)		Computes the inverse tangent of x in radians.
atanh(x)		Computes the inverse hyperbolic tangent of x.
ceil(x)		Rounds x to the next higher integer
ci(x)		Computes the cosine integral of x where x is any real number.
cos(x)		Computes the cosine of x, where x is in radians.
cosh(x)		Computes the hyperbolic cosine of x.
cot(x)		Computes the cotangent of x (1/tan(x)), where x is in radians.
csc(x)		Computes the cosecant of x (1/sin(x)), where x is in radians.
exp(x)		Computes the value of e raised to the x power.
expm1(x)		Computes one less than the value of e raised to the x power ((e^x) – 1).
floor(x)		Truncates x to the next lower integer.
gamma(x)
getexp(x)		Returns the exponent of x.
getman(x)		Returns the mantissa of x.
int(x)		Rounds x to the nearest integer.
intrz(x)		Rounds x to the nearest integer between x and zero.
ln(x)		Computes the natural logarithm of x (to the base of e).
lnp1(x)		Computes the natural logarithm of (x + 1).
log(x)		Computes the logarithm of x (to the base of 10).
log2(x)		Computes the logarithm of x (to the base of 2).
max(x,y)		Compares x and y and returns the larger value.
min(x,y)		Compares x and y and returns the smaller value.
mod(x,y)		Computes the remainder of x/y, when the quotient is rounded toward –Infinity.
pi(x)		pi(x) = x * pi
rand( )		Produces a floating-point number between 0 and 1 exclusively.
rem(x,y)		Computes the remainder of x/y, when the quotient is rounded to the nearest integer.
sec(x)		Computes the secant of x, where x is in radians (1/cos(x)).
si(x)		Computes the sine integral of x where x is any real number.
sign(x)		Returns 1 if x is greater than 0, returns 0 if x is equal to 0, and returns –1 if x is less than 0.
sin(x)		Computes the sine of x, where x is in radians.
sinc(x)		Computes the sine of x divided by x (sin(x)/x), where x is in radians.
sinh(x)		Computes the hyperbolic sine of x.
spike(x)		Spike(x) returns: 1 if x greater to zero and less than 1 0 for any other value of x.
sqrt(x)		Computes the square root of x.
square(x)		Square (x) returns: 1 if x greater to 2n and less than (2n + 1) 0 if x greater to 2n + 1 and less than (2n + 2) where x is any real number and n is any integer.
step(x)		step(x) returns: 0 if x < 0 1 if any other condition obtains.
tan(x)		Computes the tangent of x, where x is in radians.
tanh(x)		Computes the hyperbolic tangent of x.


Hardware Installation

Unpacking and Installation

1. Unpacking the lidar system

The lidar system has been carefully packaged in a wooden case to assure its secure delivery to the customer. For this purpose two wooden cases have been foreseen. One for the laser system itself and a second for the remaining parts of the lidar unit.

Inspection after shipment

Check carefully the crates for damage before uncrating the laser and the lidar system parts. Take notes of all visible external damage. To unpack the laser system follow carefully the instructions given by the laser manufacturer. To unpack the lidar system start to uncrate the upper parts first, leaving the heavier metallic pieces as the last ones to unpack. Check every component you unpack for external damage (scratches etc.). In any case, all optical material should be left in their boxes of origin since they should be unpacked only by the authorized personnel of Raymetrics S.A. during the lidar installation on site.

IMPORTANT: If you want to get the telescope assembly out of its box, DO NOT lift it by the handles which are available on the side of the cover. These handles are only for removing the cover from the telescope and not for  moving the telescope assembly while  the cover is still on.

Note: It is strongly recommended that the unpacking of the lidar and laser systems to be performed only by the authorized personnel of Raymetrics S.A. during the lidar installation on site.

Installation requirements

- Site:

For proper operation of the lidar system the ambient temperature should range between 18 and 28oC. Operation from 15 to 35oC can be assured with a chiller (optional) without any modification of the laser’s cabinet dimensions. However, it is strongly recommended to use an air conditioning unit to keep stable temperature conditions between 18-25 oC.

It is preferable that the lidar system is positioned and secured on a solid work horizontal (optical) table. When choosing a place for your lidar system, assure an opening (window) over it, with an area 15-20% larger than the total area of the emitting/receiving windows of the lidar system.

Keep always in mind:

- access should be available from all sides of the lidar system, especially to those where the alignment is performed,

- the laser remote control box access should be accessible to the lidar user
-  Choose a location for the laser and power supply and cooling unit, cabinet (PCC), such that each side of the cabinet is not less than 25-30 cm away from a wall or obstacle. Front and rear panels of the laser  should be placed at least 50 cm away from a wall or other obstacle, to allow efficient cooling of the laser head and power supply.

- Power and water services:

Power is to be 220 V or 110 V (50/60 Hz) with available average current up to 5 A or 10 A, respectively. This information is clearly indicated on the rear panel of the PCC unit. The cooling unit is a water/air heat exchanger and does not require any tap-water facility.

2. Installation of the lidar system

The on-site installation and lidar system alignment will be totally assured by the Raymetrics S.A. personnel.

Attention !

No attempt should be made by the user to install the lidar system. Damage occurring due to the non-respect of the previously mentioned instructions will not be covered under our warranty.

3. Getting started

Once all the above-mentioned steps have been fulfilled and the lidar system is fully aligned and operational, the Getting Started procedure could start on.

Safety instructions

All personnel within the lidar room must wear eye protective laser goggles, while the system is in operation. Even, low energy levels (of a few mJ) from the pulsed laser can cause irreparable eye damage.

Goggles should be at least :

Optical density 	(O.D.) >6 at 1064 nm

(O.D.) >6 at 532 nm

(O.D.) >5 at 355/266 nm

Note: It is strongly recommended that you keep a detailed Logbook on all operational details of your lidar/laser systems, and that you respect all instructions given by the lidar and laser manufacturers.


Lidar Parameters Calculation

To calculate various Lidar Parameters (see below) use the Lidar Calculation interface.

This interface is accessible by two ways.

Via Database view interface or via Surface Plot interface.

Surface Plot Interface

Select files from database interface and insert data into the surface plot.

Select a Lidar parameter from the DropDown List at the left side of the interface.

If Lidar parameters are not initialised first, a warning message appears. In this case press the “Lidar Calc” button to access Lidar Calculation interface for initialising parameters.

When inserting data to a plot or a worksheet from the database interface and selecting a Lidar parameter for exporting, the Lidar Calculation interface is appeared for initialisation.

When you press “Lidar Calc” button at the worksheet interface the Lidar Calculation interface  is slightly different as in that case wavelength, resolution, temperature and pressure parameters need to be initialised (the initialisation is done automatically when database interface is used, as this information already exists into the database).

The lidar data processing is fulfilled in two steps: (i) lidar data pre-processing and (ii) lidar inversion algorithm, which are explained hereafter.

 Step I- Lidar data pre-processing

The lidar data pre-processing is performed on the raw lidar signals. Each lidar data file (containing the average of a certain number of backscattered lidar signals S(z) coming from a distance z) is corrected for the background noise contribution (BG) due to atmospheric skylight and electronic noise of the instrumentation used. A distance square-law correction (z^2) is applied to each data point (time bin) to compensate for range-related attenuation from the atmosphere. Then, the natural logarithm of the resulting quantity is calculated. On the resulting log range-corrected signal SLOG where

,

a running low-pass derivative digital filter, with variable path is applied. The smoothing method is a running least-square fit of the dataset to the second-order polynomial, which represents a good fit for the vertically decreasing atmospheric scale height (Ancellet al., 1989)1. The spatial resolution of the measurement is related to the number 2n+1 of data points fitted to the second-order polynomial.

Step II- Lidar inversion algorithm

To retrieve the vertical profile of the aerosol backscatter coefficient (baer) at 532 nm the improved Klett inversion technique is used. This technique is based on a far-end backward iterative technique, taking into account also the atmospheric molecular contribution as described by Klett (1985). The uncertainties associated with this technique have been discussed in detail by Chazette et al.(1995) and by Boesenberg et al. (1997), while the limitations of this technique arise from an ill-posed mathematical problem (one set of signals measured with two sets of parameters to be retrieved: the aerosol extinction and backscatter coefficients) in conjunction with the a priori assumptions made for the lidar inversion, such as the fixing of the ‘reference height’ (where the atmosphere is purely molecular), and of the so called aerosol ‘lidar ratio’LR where

 .

At 355 nm the inelastically backscattered lidar signals can be inverted using the Raman inversion technique, as presented by Ansmann et al. (1992). This technique is applicable mostly under low light conditions (during early evening and nighttime) since the Raman lidar signal is sensitive to the presence of daytime background skylight.


Data Acquisition

Detection Modes

Analog detection

The analog detection mode is used to detect intense lidar signals coming from relatively short distances (typically less than 8-10 km). A transient recorder operating in the analog detection mode is based on an analog-to-digital converter (ADC), which samples and digitizes the lidar signals with a sampling rate of 20-40 MHz (depending on the type of the transient recorder used) with a 12-bit resolution. A memory length up to 8192 or 16000 time bins (Tr-xx-80 or Tr-xx-160) depending on the transient recorder type) can be selected. Each time bin corresponds to a spatial resolution of 3.75 or 7.5 m (depending on the sampling rate of the transient recorder used, Tr-20-yy or Tr-40-yy). For instance the 20 MHz sampling rate corresponds to a 7.5 m spatial resolution.

Typical lidar signals acquired in the analog detection mode is shown in Figure below

Typical lidar signal acquired in the analog detection mode.

Photon counting detection

The photon counting detection mode is used to detect very low intensity lidar signals coming from relatively large distances (typically higher than 8-10 km). Thus, the PMT is operated under single electron conditions. Flux levels as low as a few tens of photons per second can be measured. In the photon counting mode the level of the incident flux is such that the cathode emits only single electrons. The individual anode charges due to single photons are integrated to produce proportional voltage pulses, which are passed by a discriminator to a pulse counter, whose output over a pre-set time period is a measure of the incident flux.

Because of statistical fluctuations in the electron multiplication, the amplitude of the single-electron pulses is distributed according to the Poisson statistics.

To obtain a satisfactory signal-to-noise ratio (SNR) of the lidar signal in the photon counting mode, a sufficiently large number of laser shots should be obtained (normally more than 1000).

If the received lidar signal is higher than 60-100 MHz the PMT output signal should be corrected to take into account the dead-time effect. If the dead-time of the counter (ôd) is comparable to the mean interval separating two successive pulses, the counting error may be appreciable. If a dead-time correction has to be applied, then if the Nobs is the observed count rate, then the true count rate (Ntrue) corrected for the dead-time effect is given by:

Note: The value of ôd depends on the type of the PMT module used (ie. ôd = 4 ns).

Specific environmental effects may increase or decrease the count rate. For instance, background radioactivity increases it.

A typical lidar signal acquired in the photon counting detection mode is shown in figure below

Typical lidar signal acquired in the photon counting detection mode.

Note: For more details and technical specifications of the detection electronics unit, please refer to the detection electronics manufacturer Instructions Manual.


Introduction to the lidar technique

The atmospheric laser remote sensing implies the so-called light detection and ranging (lidar) technique, to probe the atmosphere up to altitudes as high as ~120 km. The development of matured pulsed laser sources has enabled the range-resolved measurements of the principal atmospheric gases and atmospheric/meteorological parameters, in a manner somewhat analogous to the radar technique. In this mode of operation a short laser light pulse is emitted to the atmosphere in one or more wavelengths (image below).

The principle of operation of the lidar technique.

The time between the transmission of the laser pulse and the arrival of the backscattered return signal is directly related to the range at which the scattering occurred. The most common processes related to laser pulse scattering by the suspended aerosol particles include the elastic Mie and Rayleigh scattering and the inelastic Raman scattering.

The atmospheric volume being probed backscatters the laser radiation and a receiving telescope is used to collect all the backscattered laser light occurring through elastic and inelastic processes. Wavelength-separation units are used to spectrally separate the lidar signals at various wavelengths and to reject the atmospheric background radiation. The lidar signals are then fed to fast detectors (photomultiplier tubes: PMTs). The PMT output signals after amplification and digitization are sent to a central personal computer for further processing and storage.

The lidar observations of suspended aerosol particles can be made remotely with high spatial and temporal resolution using the lidar technique. The lidar systems can be operated from gound or mobile platforms, such as aircrafts, helicopters or satellites.

The basic lidar equation is given below:

          (1)

where, P(z) is the power incident on the receiving optics from distance z, [image] is the laser output power, ô is the duration of the laser pulse, c is the velocity of light, [image] is the volume backscattering coefficient, [image] is the extinction coefficient of the atmosphere and [image] is the receiving telescope aperture.  is the so-called geometrical form factor (or overlap factor). This factor represents the probability of radiation in the target plane at range z reaching the detector, based on geometrical considerations. The 1/z2 dependence leads in many applications to a signal-amplitude dynamic range that extends over several decades. Therefore, two detection modes are used: the analog detection mode and the photon counting operation mode.

The detection of the suspended aerosol particles can be performed by an elastic lidar system (single or two-wavelengths) or by an inelastic (Raman) lidar system. The elastic backscattered lidar signals can be inverted using the Klett’s inversion algorithm, while the inelastically backscattered lidar signals can be inverted using the Raman inversion technique, as presented by Ansmann et al. (1992)


Klett, J., “Lidar inversion with variable backscatter/extinction ratios”, Applied Optics, 24, 1638-1643, 1985


Chazette, P., David, C., Lefrere, J., Godin, S., Pelon, J. and Megie, G., Comparative lidar study of the optical and dynamical properties of stratospheric post-volcanic aerosols following the eruption of the El Chichon and Mount Pinatubo, J. Geophys. Res., 100, 23, 195-207, 1995


Boesenberg, J., Timm, R., and Wulfmeyer, V., Study of retrieval algorithms for a backscatter lidar. Final Report, MPI Report No 226, pp. 1-66, 1997


Ansmann, A., U. Wandinger, M. Riebesell, C. Weitkamp, and W. Michaelis, “Independent measurements of extinction and backscatter profiles in cirrus clouds using a combined Raman elastic-backscatter lidar,” Applied Optics, 22, 2257-2264, 1992


Ancellet, G., A. Papayannis, G. Mégie, J. Pelon, "Tropospheric Ozone Measurements Using a Nd:YAG Laser and the Raman Shifting Technique", Journal of Oceanic and Atmospheric Technology, 6, 832-839, 1989.


Measures, R., Laser Remote Sensing: Fundamentals and Applications, Wiley, New York, 1984