United States
                Environmental Protection
                Agency
 Environmental Monitoring
 Systems Laboratory
 Las Vegas, NV 89193-3478
                Research and Development
 EPA/600/S4-91/014  Aug. 1991
EPA       Project  Summary
                Wetlands  Detection  Methods
                 Investigation
                K. H. Lee
                  The purpose of this investigation was
                to research and document the applica-
                tion of  remote sensing technology to
                wetland detection and mapping. Vari-
                ous remote sensing sensors and plat-
                forms are evaluated  (1) for suitability
                to monitor specific wetland  systems;
                (2) for  their effectiveness in detailing
                the extent of wetlands; (3) for their ca-
                pability to monitor changes; and (4) for
                the  resulting relative  cost-benefits of
                implementing and  updating  wetlands
                databases.
                  The environment to be monitored
                consists of physiographic and ecologi-
                cal wetland resources affected directly
                or Indirectly by anthropogenic activity.
                Aircraft and satellite  remote sensing
                can  be  used to record and assess the
                condition of these resources. Monitor-
                ing  of  environmental conditions is
                based on the observation and interpre-
                tation of certain landscape  features.
                Although some forms of monitoring are
                continuous, resource monitoring from
                aircraft  and satellite platforms Is peri-
                odic in nature, with change being docu-
                mented through  a  series of observa-
                tions over a given span of time.
                  This report summarizes the findings
                of a bibliographic search on the meth-
                ods  used to  inventory and/or  detect
                changes in wetland environments.  The
                bibliography contains numerous cita-
                tions and is  not intended to be all-
                inclusive. Books, major journals, and
                symposium proceedings were  exam-
                ined.  The findings documented  will
                provide the potential user with a basic
                understanding of remote sensing tech-
nology as it is applied to wetland moni-
toring and trend analysis.
  This Project Summary was developed
by  EPA's Environmental Monitoring
Systems Laboratory, Las Vegas, NV, to
announce key findings of the research
project that Is fully documented In  a
separate report of the same title (see
Project Report ordering Information at
back).

Introduction
  The purpose of this report is to present
an overview of wetlands mapping proce-
dures, emphasizing the role of  satellite
and aircraft imagery and their interpreta-
tion; field verification;  and compilation of
all these data. The procedures for map-
ping changes in the extent and types of
wetlands is  generally based  on  a com-
parison of earlier (historical) remote sens-
ing imagery to recent imagery.
  The detail, accuracy, and precision of
the mapping depends on what results are
desired from the final report; the availabil-
ity of the necessary remote sensing data;
the technical personnel and equipment on
hand;  and the  specific budget  for  the
project.
  Wetlands are difficult to map because
of (1) water level fluctuations, (2) the many
differing types of wetland settings, (3) the
difficulties of ground travel in placing geo-
graphic control point markers in this soggy
terrain, and (4) the changes in the bound-
aries of wetlands types caused by varia-
tions in the hydrologic cycle with  its sea-
sonal, annual, and long-term fluctuations.
Furthermore,  other changes  may have
been created by anthropogenic  factors,
                                                                  Printed on Recycled Paper

-------
                United States
                Environmental Protection
                Agency
 Environmental Monitoring
 Systems Laboratory
 Las Vegas, NV 89193-3478
                Research and Development
 EPA/600/S4-91/014  Aug. 1991
EPA        Project  Summary
                Wetlands  Detection  Methods
                 Investigation
                K. H. Lee
                  The purpose of this investigation was
                to research and document the applica-
                tion of  remote sensing technology to
                wetland detection and mapping. Vari-
                ous remote sensing sensors and plat-
                forms are evaluated  (1) for suitability
                to monitor specific wetland  systems;
                (2) for  their effectiveness in detailing
                the extent of wetlands; (3) for their ca-
                pability to monitor changes; and (4) for
                the  resulting relative  cost-benefits of
                implementing and  updating  wetlands
                databases.
                  The environment to be monitored
                consists of physiographic and ecologi-
                cal wetland resources affected directly
                or indirectly by anthropogenic activity.
                Aircraft and satellite  remote sensing
                can  be  used to record and assess the
                condition of these resources. Monitor-
                Ing  of  environmental conditions is
                based on the observation and interpre-
                tation of certain landscape  features.
                Although some forms of monitoring are
                continuous, resource monitoring from
                aircraft  and satellite platforms is peri-
                odic in nature, with change being docu-
                mented through  a  series of observa-
                tions over a given span of time.
                  This report summarizes the findings
                of a bibliographic search on the meth-
                ods used to  inventory and/or  detect
                changes in wetland environments.  The
                bibliography contains numerous cita-
                tions and is  not intended to be all-
                inclusive. Books, major journals,  and
                symposium proceedings were  exam-
                ined.  The findings documented  will
                provide the potential user with a basic
                understanding of remote sensing tech-
nology as it Is applied to wetland moni-
toring and trend analysis.
  This Project Summary was developed
by  EPA's Environmental Monitoring
Systems Laboratory, Las Vegas, NV, to
announce key findings of the research
project  that Is fully documented In a
separate report of the same title (see
Project  Report ordering Information at
back).

Introduction
  The purpose of this report is to present
an overview of wetlands mapping proce-
dures, emphasizing the role of  satellite
and aircraft imagery and their interpreta-
tion; field verification;  and compilation of
all these data. The procedures for map-
ping changes in the extent and types of
wetlands is  generally based  on  a com-
parison of earlier (historical) remote sens-
ing imagery to recent imagery.
  The detail, accuracy, and precision of
the mapping depends on what results are
desired from the final report; the availabil-
ity of the necessary remote sensing data;
the technical personnel and equipment on
hand;  and the  specific budget  for  the
project.
  Wetlands are  difficult to map because
of (1 ) water level fluctuations, (2) the many
differing types of wetland settings, (3) the
difficulties of ground travel in placing geo-
graphic control point markers in this soggy
terrain, and (4) the changes in the bound-
aries of wetlands types caused by varia-
tions in the hydrologic cycle  with  its sea-
sonal, annual, and long-term fluctuations.
Furthermore,  other changes may have
been created by anthropogenic  factors,
                                                                  Prated on Recycled Paper

-------
 such as encroaching urban and  agricul-
 tural developments; by stream channel al-
 terations; and drainage and damming con-
 structions.
   To avoid the problems associated with
 seasonal changes in wetland boundaries,
 both the remote sensing data  and the
 field verification  data should be collected
 at the same time of the year so that the
 same boundaries will be in the same geo-
 graphical positions.

 Procedures
   The major part of mapping the wetlands
 is generally done through the  interpreta-
 tion of remote sensing imagery.  This  is
 considered here to be the satellite imag-
 ery, airborne radar imagery, airborne  multi-
 spectral  digital  imagery, vertical  overlap-
 ping aerial photographs (black and white,
 color, and color infrared [CIR]), and to a
 minor extent color photographs (in hand-
 held cameras) and video tapes taken from
 aircraft.
   Satellite imagery has a small scale, and
 generally cannot be viewed stereoscopi-
 cally.  This contrasts with aerial photo-
 graphs which have a much  larger scale,
 ranging normally from about 1:10,000 to
 1:58,000, and  which can be viewed ste-
 reoscopically.
   The larger scale of the aerial photo-
 graphs with its smaller mapping units of
 wetlands cannot be correlated directly with
 the  larger units  of the satellite imagery.
 This problem can be largely overcome by
 combining the smaller units (from the aerial
 photographs) until they correspond to the
 larger units of the satellite imagery.  This
 correspondence  has been as high as 90
 percent in some  studies.
   Several different types of satellite imag-
 ery are available: the MSS (Multispectral
 Scanner) has four spectral bands: visible
green, visible red, and two reflectance in-
frared bands  having about  an 80-meter
ground resolution.
  The TM (Thematic Mapper) satellite has
six spectral bands with a 30-meter resolu-
tion, and a thermal infrared  band with  a
 120-meter resolution.  Both  these satel-
 lites are in polar orbits  and can collect
spectral information every 16 days  over
the same surface area.
  TM is  better suited for wetlands map-
 ping than the MSS because of better spa-
tial resolution (30 m), seven narrower spec-
tral bands sensitive to differences in spec-
tral reflectance of vegetation,  and a higher
 level of quantization (i.e., digital  numbers
for TM = 256, for MSS = 128).
   SPOT satellite imagery (a French satel-
 lite)  has a 10-meter black and white reso-
 lution, and a 20-meter resolution for three-
 band multispectral images; this is a  finer
 resolution than the LANDSAT MSS and
 TM  images, but  it has a fewer spectral
 bands and a smaller areal coverage.  This
 satellite can be oriented during its orbit so
 as to  produce stereoscopic coverage; it
 has a repeat cycle of  26  days.   SPOT
 data can be integrated with  LANDSAT TM
 data to  provide  a composite  view,  up-
 graded by  the finer  spatial  features  of
 SPOT and the finer spectral resolution of
 TM.
   One advantage of  satellite  imagery is
 color enhancement of scenes to empha-
 size certain features of the landscape, such
 as different types or stages of vegetation,
 etc;  this  procedure is useful  in wetlands
 interpretation.  Conversely, the  stereo-
 scopic exaggerated relief (normally about
 three or four times) observed in the stereo
 images of the normal aerial photographs
 can  help to  delineate the low-lying areas
 of wetlands.
   Many series of  aerial photographs are
 available for most areas in  the  States.
 Typical scales normally range from around
 1:10,000 to 1:58,000.   An ongoing  pro-
 gram by the USGS will cover the entire
 United States  with small-scale  CIR
 1:58,000 aerial photography.   The  CIR
 photography seems  to  be  the preferred
 type for most landscape characterization
 (which includes wetlands mapping).
   The above indicates the  many options
 in remote sensing imagery available, and
 the planning necessary to select the most
 advantageous imagery for primary baseline
 mapping.  To map the changes over time
 in wetland areas,  historical aerial photo-
 graphs are generally used; these can ex-
 tend back as much as 50 years. A series
 of these older photographs  can show the
 development and trend of the present sta-
tus of the wetlands now  being mapped.
   Side-looking radar is little used for wet-
 lands mapping but has  been  successful.
 Video  imagery has been little  used, its
 resolution less than  aerial  photography.
 Further work on optimizing spectral bands
 must be done before video can be used
 as an additional data source.

 Previous Mapping
   Previous mapping of wetlands provides
information on any later changes in the
character of the wetlands. However, three
serious problems  in  integrating previous
wetlands  data into current mapping are:
  1)  The classifications  can be based on
     different  criteria so that the units
     mapped previously are not the same
     as  those being  mapped for  the
     present project.
  2)  The areal precision of ground con-
     trol points predating Global Position-
     ing  Systems  (GPS) is usually  poor
      for correlating any specific feature,
      point, or contact with later mapping.
      Compilation of such data is not fea-
      sible in many cases.
  3)  The  differences in scales between
      the previous mapping and later map-
      ping  may make correlations difficult
      if not impossible; this may also con-
      trol the differences in the ground or
      spectral criteria included in the vari-
      ous wetlands  classifications.

   A classification  system  developed  by
 the  USGS  in 1976 covers all  remotely-
 sensed resource data,  not  just the wet-
 lands.  A  wetlands classification system
 (Cowardin System) was developed by the
 Forest Service  in 1979 to replace a 1955
 system, and is largely used or modified.

 Field Verification
   Until recently, the problem of locating
 field geographic control points exactly has
 been a major problem.  The seasonal or
 annual changes in this water-dominated
 environment, plus  even changes by indi-
 vidual storms and the general  thick veg-
 etation cover, together with the difficulties
 of field personnel  movement within  the
 wetlands, can prevent the establishment
 of adequate recognizable control points.
   The one outstanding technical develop-
 ment which apparently overcomes much
 of this problem is the development of GPS
 developed by the US military.
   At the present time, the  satellite data
 are  available only  during a certain few
 hours  in the day so that field work must
 be coordinated to take advantage of the
 specific schedules of the satellites to  re-
 ceive their transmissions for site control.

 Geographic Information System
   The Geographic  Information System
 (GIS) is distinguished from other data man-
 agement systems by its ability to perform
 spatial analyses with multiple levels of data
 in a  selected geographic area.  The GIS
 is a convenient and organized method  for
 analysis of wetlands and allows for a co-
 hesive database into which additional  in-
formation can be incorporated and refine-
 ments made.
  Computerized GISs are widely utilized
to store, query, retrieve, display, and man-
age  large  amounts of  digital  data  as-
sembled from many sources.  The ability
to geometrically transform  and integrate
multiple data types is very important when
accounting for differences in scale, map
projections, spatial resolutions, and carto-
graphic coordinate systems.
  Both the raster and vector systems are
used in the GIS. For example, geometric
or overlay (point) operations  are easier to
                                                                          &U.S. GOVERNMENT PRINTING OFFICE: 1991 - 548-028/40062

-------