N Water 
Mixing 
do not 
Species, 
sample 
  
Fluorescence emission spectra of oil dispersed in water 
exhibit more complex structure comparatively to spectra 
of pure mineral oils. Under shortwave excitation several 
maxima are presented in emission spectrum of water 
mixed with oil. For example, pure gasoline has the only 
one fluorescence maximum located at 290 nm, but 
spectrum of sample of gasoline in water presents two 
maxima at 290 and at 330 nm. 
For oil dispersed in water emission maximum location 
and spectral shape strongly correspond with excitation 
wavelength. Basic bands in fluorescence emission 
spectrum for mineral oils dispersed in water are located 
at 290, 330.340 and 400.450 nm. The number of 
bands in emission spectrum, and ratio of their 
intensities vary for different mineral oils, and could be 
used for oil type classification. 
3. FLUORESCENCE OF DISSOLVED ORGANIC 
MATTER 
Naturally occurring organic compounds are found in 
significant concentrations in water throughout the 
world. Many organic chemicals found in natural waters 
can be regarded as products of both biosynthesis and 
biodegradation. Until now not more than 30% of 
dissolved organic -matter have been chemically 
characterized. 
For natural water samples two spectral components are 
observed with excitation below 270 nm. The first 
component with maximum at 340 nm is called in 
literature "protein-like fluorescence". The second one is 
caused by humic substances, and has blue fluorescence 
with maximum located at 400...460 nm depending on 
excitation wavelength. For the last component the 
emission maximum is practically constant while 
excitation wavelength is varying from 200 to 308 nm 
(with small blue shift of maximum when excitation is 
changed from 270 to 308 nm). With rising the 
excitation from 308 nm to higher wavelengths, the 
position of the emission maxima for all natural water 
samples shifts towards longer wavelengths. Models of 
the nature of fluorescence of dissolved organic matter 
have been developed to explain this phenomenon. The 
distinctive features of spectra behaviour with excitation 
alteration can be used to distinguish dissolved organic 
matter naturally occurring, in water and oil pollution. 
On the basis of experimental results we can propose the 
lidar system for oil spill diagnostics with two excitation 
wavelengths. There is a special need in using, more than 
one wavelength for excitation. Oil in film, oil dispersed 
n Water, and dissolved organic matter become 
distinguishable if we use different spectral ranges for 
Spectra excitation. 
571 
The first excitation wavelength must be chosen from the 
spectral region 220...270 nm. Analyzing emission at 
340 nm we can estimate the concentration of oil fraction 
dispersed in water, and also detect the presence of light 
oil products emitting at 290 nm. The second excitation 
wavelength for diagnostics of crude oils must be 
selected from the spectral range of 350...400 nm. The 
excitation at this wavelength can be used also for 
discrimination between oil pollution and dissolved 
organic matter of natural origin. 
4. MEASUREMENT OF OIL FILM THICKNESS 
For oil film thickness estimation it is possible to use a 
suppression by an oil film of the integral intensity of 
water Raman stretching band (Kung, 1976). The ratio 
of water Raman signals over and outside the oil slick, 
RR, can be used to calculate the oil film thickness d, 
if the extinction coefficients at excitation and Raman 
wavelengths, k, and k,, are known (Hoge, Swift, 1983): 
d — -I/(k,*- ky) In (R'/R) (1), 
Hoge and Swift (1983) have applied a nitrogen laser to 
excite Raman signal of natural ocean water beneath the 
oil slick from an altitude of 150 m. In the cited 
reference the water Raman spectrum excited at 337 nm 
is strongly affected by fluorescence background from oil 
film. Hengstermann and Reuter (1990, 1992) have used 
the described technique for oil film thickness estimation 
from an altitude of 300 m by means of the airborne laser 
fluorosensor with excimer laser operating at 308 nm. 
There are some problems in implementation of the 
technique of integral water Raman suppression for 
estimation of oil film thickness. Remotely detected 
signal depends on such experimental conditions as laser 
power accidental variation, laser beam penetration into 
the water column, turbidity of water column and others. 
To minimize the influence of experimental conditions 
on estimated thickness of oil film on water surface we 
offer another technique which uses contour analysis of 
water Raman spectrum. 
The Raman backscattered signal from water molecules 
is used in remote fluorescent techniques as an internal 
standard to minimize the effect of laser beam 
penetration into the water column. The other usage of 
water Raman band is measurement of temperature and 
salinity of sea water. The method is based on 
dependence of spectral shape of OH Raman stretching 
band 3100..3700 cm”! on water temperature and 
salinity. Though this dependence is considerably weak, 
the use of "least squares method" or mathematical 
"reduction method" has allowed us to achieve good 
results in temperature and salinity evaluation both in 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996