seasat-A 
jea-surface 
tions for 
rties of 
rrains and 
hness on 
rom 
t when 
t or by 
r (FLD) 
ging 
“he 
yof 
Imi- 
| per 
gnitude 
in the 
noma- 
num 
3 near- 
and 
cover 
when 
| and 
tural 
ttle 
ermit 
  
  
  
   
  
   
    
   
     
   
   
  
  
   
  
  
  
  
  
  
  
   
  
   
    
   
     
  
  
   
   
   
  
   
   
  
   
   
expressed in terms of rhodamine dye equivalency at the wavelength of 
several Fraunhofer lines. The FLD detectivity may be assessed at each 
Fraunhofer line, and the optimum line for field observation of the 
material may be selected. 
Future work will include the integration of the FLD with a line 
scan imaging system in order to assess the contribution of two- 
dimensional spatial resolution to the interpretability and usefulness 
of luminescence data. It should also include: 1) Investigation of 
luminescence polarization of some materials, particularly metal 
stressed plants; 2) an assessment of the use of pulsed lasers to 
stimulate phosphorescence decay time in the nanosecond and microsecond 
ranges; and 3) a study to determine the feasibility of conducting an 
FLD experiment from the Space Shuttle. 
Laboratory and field study of the measurement and interpretation 
of luminescent materials began in 1964, with experimental work using 
an active ultraviolet imaging system (Hemphill and others, 1965). This 
work led to the development of a prototype Fraunhofer line discriminator 
(FLD); an airborne remote sensing tool for measuring luminescence. The 
FLD was designed to operate on the Fraunhofer line depth principal 
(Kozyrev, 1956; Grainger and Ring, 1962) which uses the sun as an exci- 
tation source and permits detection of luminescing materials under 
daylight conditions. Experiments with the instrument showed that 
selected materials, such as luminescing tracer dyes, could be detected 
in very small quantities (Hemphill and others, 1969; Stoertz and others, 
1969). 
In order to predict optimum wavelength and sensitivity requirements 
for detection of materials other than rhodamine WT, luminescence of a 
variety of materials was measured with a laboratory fluorescence spec- 
trometer in terms of rhodamine WT, used as a laboratory standard. These 
results, coupled with those obtained with the prototype FLD, were used 
as a basis for engineering a redesigned FLD with-an order of magnitude 
increased sensitivity. This redesigned model, built by the Perkin Elmer 
Corporation operates at three discrete Fraunhofer lines, hydrogen B at 
486.1 nm, sodium D at 589.0 nn, and hydrogen a at 656.3 nm and has the 
sensitivity to detect rhodamine WT dye in concentrations as low as 
0.1 ppb in 1/2 m of water at 20° C. An additional system built by 
Isomet Electronics uses a tunable acoustical optical filter which permits 
tuning to an accuracy of less than 0.5 nm with an average bandwidth of 
less than 0.1 nm. The sensitivity of this instrument is approximately 
an order of magnitude less than the Perkin Elmer FLD. 
Measurements have heen made on a variety of natural materials and 
on selected luminescence and reflectance standards. The rhodamine WT 
equivalent luminescence of each standard as measured with the FLD was 
confirmed with a laboratory fluorescence spectrometer.