A first-cut assessment of the trophic status of inland lakes in Wisconsin was obtained from LANDSAT data. To satisfy the criteria of the project, a large and versatile computer program was developed to gain access to LANDSAT data. This analysis technique has proven to be a cost-effective method of classifying inland lakes in Wisconsin

Fisher, L. T.

Scarpace, F. L.

English

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TROPHIC STATUS OF INLAND LAKES FROM LANDSAT 
By Lawrence T. Pisher and Frank L. Scarpace, Ins t i tu te  for  Environmental Studies, 
University of Wisconsin, Madison, Wi3consin 
ABSTRACT 
A cooperative program between the  Wisconsin Department of Natural Resources and the 
University of Wisconsin's Ins t i tu te  f o r  Environmcntal Studies has resulted in  a f i r s t - cu t  
assessment of the trophic s ta tus  of inland lakes in  Wisconsin from LANDSAT data. To s a t i s f y  
the c r i t e r i a  of the project, a large and versati2e computer program t o  gain access t o  LANDSAT 
data was developed. This analysis technique has proven t o  be a cost-effective method of 
classifying inland lakes in Wisconsin. 
INTRODUCTION 
The Wisconsin Deportment of Naturh? Resources (DNR) i s  required to  c lass i fy  the lakes 
i n  the s t a t e  as  t o  the i r  trophic level i n  response t o  the federal legislat ion "Federal Water 
Pollution Control Act Amendments of 1972," section 314. 
This paper describes a cooperative ef for t  between DNR and the University of Wisconsin's 
I n s t i t u t e  for  Environmental Studies (IES) t o  extract  LANDSAT data providing a reasonable 
measure of trophic s ta tus  in  a cost-effective manner. An additional resul t  has been the 
design of a highly versa t i le  interactive graphics computer program available fo r  both research 
and agency use. 
LANDSATt s mu1 t i spect ra l  scanner (MSS) simultaneously gathers data a t  four d i f ferent  
wavelengths: Band 4 ( $ 5  t o  .6u), Band 5 (.6 t o  .7u), Band 6 ( - 7  t o  .8u), and Band 7 ( - 8  t o  
1 . 1  A swath 185 km (115 mi) wide i s  scanned during each orbi t ,  and t h i s  i s  sampled a t  
intervals so  that  data is recorded fo r  d iscre te  picture elements or pixels whose dimensions 
a re  approximately 50 x 70 M. 
In th i s  project, Band 5 data was desired because values there can be correlated f a i r l y  
accurately with lake turbidity.  Band 7 data was used to  form "pictures" of lakes on a 
computer terminal. From these, the computer program allowed the terminal operator t o  se lec t  
individual picture elements whose data values were punched on cards. 
Data was extracted in t h i s  fashion for  a l l  Wisccnsin lakes with areas . ,eater than 20 
acres and depths greater  than eight fee t  -- about 3000 lakes in a l l .  The r ~ i u l t i n g  cards 
were sorted, and lakes within each of Wisconsin's 72 counties were ranked in  order of 
decreasing average Band 5 values. 
LAKE TURBIDITY AND LANDSAT DATA 
An e a r l i e r  project (1) investigated relationslrips between LANDSAT Band 5 brightnesses 
and lake turbidity.  In t h i s  project, 37 lakes included in  eight  different  LANDSAT scenes 
were studied (Figure 1) .  The northern Wisconsin lakes were generally c lear  and oligotraphic; 
those i n  the souther1 part  of the s t a t e  range from moderately t o  highly eutrophic. 
Secchi depth readings for  each of these lakes were obtained by DNR personnel, but it 
was operationally not possible t o  coordinate these t e s t s  with LANDSAT overfl ights.  In some 
instances, over a month's difference existed between secchi depth acquisition and a suitably 
cloud-free WWDSAT orb i t .  
Figure 2 shows correlation between LANDSAT Band 5 data and secchi depths for  some of 
these lakes. A def in i te  correlation i s  evident, and much of the sca t t e r  i s  f e l t  t o  be due 
t o  the time differences described above. 
https://ntrs.nasa.gov/search.jsp?R=19760010408 2020-03-22T16:17:04+00:00Z
CWUTER PROCESSING OBJECTIVES 
Originally t h i s  project involved the densitometric analysis of the  photographic rendition 
of the IANDSAT imagery f o r  a l l  the Iarge lakes i n  Wisconsin. Difficult ies with radiometric 
quali ty of 9x9 inch photography and operational problems due t o  extrenely small image sizes 
of  small lakes on 7- imges  prompted us t o  begin development of computer-assisted analysis. 
Since then, we have expanded the program t o  provide a highly versati le ,  general purpose 
ns l t i spect ra l  analysis and dot? a q u i s i t i o n  tool f o r  several users and applications. 
The objectives that  were envisioned i n  the design of  the  program were: 
a) Access t o  small, highly specific subsets of large  data s e t s  was needed. We wanted 
t o  be able t o  se lec t ,  f o r  example, an accurately l o c a t d  s ingle  data point i n  a bay 
of  a lake. 
b) Miltispectral analysis capabil i t ies were needed fo r  feature selection tzsks. 
c) Operatim. needed to  be highly interactive,  s o  tha t  options could be selected o r  
changed easily, or  feature selection t ra in ing c r i t e r i a  eas i ly  a l tered under operator 
sup~rvis ion,  etc. 
d) Operator-recognizable displays were needed, f o r  example, t o  recognize and distinguish 
lakes, o r  t o  estimate acceptabil i ty o f  an exper ien ta l  c lass i f ica t ion.  
e) Navigatimal aids were needed t o  help loczte areas of in teres t .  
f) Data histograming capability was designed t o  a s s i s t  in  supervised training fo r  
f e a k r e  s Aection. 
g) Use with a variety of  data types was desirable. A t  the  moment, the program is being 
used both with LANDSAT data and digi t ized ae r i a l  photography. 
h) The program had to be a t t r ac t ive  t o  a wide range of users. This implied tha t  
operation -hould be eas i ly  learned and that  the program he extremely t ~ l e r a n t  of 
operator e n  ors . 
i )  No capital  was available fo r  hardware. We were constrained t o  use exist ing equipment 
INTERACTIVE GRAPHICS PROGRAMING SYSTEM 
de elected t o  design the program around an interactive graphics terminal, and the Madison 
Acade!nic Computing Center's Univac l l i O  computer. One reason was tha t  several terminals are  
available on campus and a r e  given excellent software and hardware support. Secoad, the 
a b i l i t y  t o  prodlvcp a television-type image during proglam execution, ?nd the  operator's 
a b i l i t y  t o  r espnd  to the display, provided us with the man-machine I i~teract ion deemed 
essential .  Third, graphics features allowed operator snecificat 'on of data coordinates, 
graphical display of data histbgral.;, and similar  nm-alphanumeric input and output. 
Xe read and decoie ml t -spect ra l  data for a f a i r l y  large area, retaining data for whatever 
bmds are desired and reading data tapes a t  any of several possible resolurions. Then a 
pcrtion of th i s  data i s  displayed on the terminal by means of an array of  characters. Each 
character AS displayed only i f  a s e t  of t e s t s  upon the m l t i s p e c t r a l  data is passed. Complete 
f l ex ib i l i ty  is provided i n  the s e l - ? c t i o ~ ~  cf  characters, b a d s  t o  be tested,  and t e s t  bounds; 
a l l  of those can be altered at  appropriate points during cpzration. 
Disi'liys can be 1oca:ed a;ywheAL within the region for which data was extracted, and can 
Lc: shown a t  any of several res;;lutians. New displays can bt? called a t  any time, pcrhapr. a t  
different  resolutions or with different  character ' . ts  or  5ounds. 
Civen a display, data can be extracted s i ~ g l y  by pointing a t  desired points o r  blocks of 
4F" 
points. Data fo r  a l l  such points is printed, punched if desired, and written in to  a catalogued 
f i l e  wnich is available t o  any other program f o r  additional analysis. 
Line pr in ter  "maps" duplicating displays and showing a l l  extracted data points can be 
produced as desired. 
Interactive computer terminals a re  becoaing familiar i n  many applications including 
remote sensing data analysis. A typical  t e n i n a l  consists of  a typewriter keyboard and some 
form of output device -- usually a typewriter, teletype, o r  cathode-ray tube display. 
Programs can be written so tha t  interruptions occur at points where operator intervention is 
needed. keyboard responses can allow selection of options, decisions, o r  input of  needed 
data, usually in  response t o  something computed and displayed by the  terminal. Such f a c i l i t i e s ,  
with proper programming, can provide substantial  ve r sa t i l i ty  and convenience. 
Graphics terminals, now becoming collgon, add some powerful features t o  basic in teract ive  
terminals. In addition t o  display o r  input o f  alphanumeric c!aracters, they allow computer- 
produced drawin~s  of points o r  l ine  segments, and operator input of coordinate positions 
which can be formed in to  graphs, outl ine drawings, o r  complex figures. %e,v a lso  allow f a r  
transmission of graphical o r  two-dimensional data to  the computer. 
DATA EXTRACTIW TECHNIQUES 
After locating approximate coordinates of lakes by inspection of 9x9 inch imagery, data 
from Bands S and 7 was extracted. Displays were formed by "level sl icing" on Band 7, s ince 
very low infrared reflectance of water causes extremely low brightnesses i n  that  band. 
Although the displays were subject t o  a large number of geometric distort ions,  it proved 
generally easy for  the terminal operator t o  recognize and identify lakes and t o  decide where 
to extract  data. 
Data points were then selected, with an average of three t o  f ive  points per lake. I f  
ground t ru th  data were available from specified portions of a lake, o r  depth problems were 
known t o  exis t ,  an e f fo r t  was made t o  extract  data from an appropriste region of the lake. 
Printer  naps were produced t o  provide a documentary record; these show a l l  lake names and 
data points. A t  the end of each run, printed and punched data output was produced. 
Typically, one t o  three LANDSAT CCTs (each comprising a quarter  of a scene) were analyzed 
i n  each day's operation -- these might include anywhere from one o r  two up t o  50 lakes apiece. 
Eco?omics of operation were highly dependent upon the number of lakes per scene since tape 
reading was a major part  of computation expense. Detailed costs during a typical  production 
..UI are  shown in Figure3 . Tnis n m ,  las t ing 75 minutes, involved loading one tape and 
reading only one portion of it. Ten f u l l  and pa r t i a l  displays, and nine pr in ter  maps (each 
including a t  l eas t  one lake) were produced. The t o t a l  computation charge (using l a t e  night 
computer rates)  uas jus' under $6.00. 
Ovc'rall, about $4,000 of computer time and $6,000 f o r  operator sa lar ies  were requi-ed 
t o  obtain data for the 3,0d3 lakes. 
PRODUCTS AND COXCLUSIONS 
Results supplied to  DNR inc!ude, f i r s t ,  a machine-produced tabulation of lakes i n  each 
of 72 counties, l i s t ing  in order of decrssring Band reflectance and therefore a t  leas t  
approxi.mately in order of decreasing turbidity;  and a 35mm microfilm copy of a l l  pr in ter  maps 
produced, showing locations of a l l  data points. A samt . .  output fo r  one countv i s  included 
in Table I .  
Another resul t  has been tile -nmrl:ter program icse ' f ,  which i s  now being used for research 
ac t iv i t i e s  by DNR personnel. ! , - lpzte tha t  i t  w i l l  become an operational tool used by 
DNR s t a f f  for similar  o r  related , .*lysis. 
FUTURE WORK 
A much more extensive ground t ru th  e f fo r t  is now being planned, i n  which DNR f i e l d  s t a f f  
w i l l  be obtaining secchi depths and related data in  conjunction vi th  LANDSAT overflights. 
kvigat ion procedures are  being developed t o  allow coordinate transformations f w n  scene 
t o  scene. These w i l l  be used t o  inexpensively obtain additional data over the course of a 
f u l l  season. Also, data from bands other than Band 5 w i l l  be incorporated. This multispectral 
mul t i t eqora l  analysis is e x ~ s c t e d  t o  yield be t t e r  measures of  trophic s ta tus .  
A cooperative ; rogram involving University researchers and natural  resource managers 
has u t i l i zed  IANDSAT data t o  p d u c e  an economical trophic s t a tus  assessment of 3000 Wisconsin 
lakes. Computer programs have been developed which allow easy, rapid access t o  LANDSAT data 
and which can be used by non-research personnel fo r  production data extraction. Capital 
expenses a r e  low, and operating costs  a r e  very reasonable compared t o  expenses t o  acquire 
on-si te data of  comparable quality. 
REFERENCES 
1. F. Scarpace, L.T. Fisher, and R. Wade, "Lake Clas t i f ica t ion Using ERTS Imagery," Proc. 
Symp. on Rearote Sensing and Photo Interp., Comn. G ,  ISP, Banff, Alberta, Canada, Oct. 1974. 
2. A.N. Williamson, "?fapping Suspended Para.icle and Solute Concentrations from S a t e l l i t e  
Data," U.S. Army Engineer Waterways Experiment Stat ion Report (1974). 
TABLE 1.- SAMPLE OIJTPUT SUPPLIED TO DNR: ALL LAKES I N  COLUMBIA COU,WY 
RANKED I N  DECREASING ORDER OF AVEMGE BAND 5 REFLECTANCE 
BAND 5 RANGE 
16 - 18 
14 - 17 
14 - 15 
14 - 15 
14 - 14 
13 - 15 
13 - 14 
13 - 14 
13 - 14 
13 - 14 
13 - 13 
RANK 
1 
2 
3 
4 
5 
6 
SCENE IDENTIFICATION 
1378-16151 3 
1378-16151 3 
1378-16151 3 
1378-16151 3 
1378-16151 3 
1378-16151 3 
1378-16151 3 
1378-16151 3 
1378-16151 3 
1378-16151 3 
1378-16151 3 
NUMBER OF POINTS 
4 
2 
3 
4 
3 
9 
2 
2 
2 
2 
1 
LAKE NN.2 
Swan 
Long 
Lazy 
Park 
Spring 
Lake Wisconsin 
E N D  5 AVERAGE 
16.50 
15.50 
14.67 
14.50 
14.00 
14.00 
13.50 
13.50 
13. 50 
13. 50 
13.00 
7 I Beckel. 
8 
1 9  
1 10 
11 
Si lver  
George 
Wyona 
Crystal 
Figure 1--Map of Wisconsin Showing Locations of Lakes Sampled by the 
Wisconsin Department of Natural Resources 
SECCHI DEPTH 
Figure 2--Correlation Between Band 5 Brightnesses and Secchi Depths 
for 1 7  Test Lakes 
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Trophic status of inland lakes from LANDSAT

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