13 Water Quality
291
13.4 Case Studies
Remote sensing applications to water quality are limited to measuring those substances or conditions that influence and change optical and/or thermal characteristics
of the apparent surface water properties. Suspended sediments, chlorophylls (algae),
DOM (humus), oil, and temperature are water quality indicators that can change the
spectral and thermal properties of surface waters and are most readily measured by
remote sensing techniques. Substances (i.e., chemical) that do not change the optical
and/or thermal characteristics of surface waters can only be inferred by modelling
using other surrogate properties (i.e., suspended sediments, chlorophylls) which may
have responded to an input or reduction of chemicals. Examples of applications of
remote sensing for measuring suspended sediments, chlorophylls, oils, and temperature will be given.
13.4.1 Suspended Sediments
Suspended sediments are the most common pollutant both in weight and volume in
surface waters of freshwater systems (Lal, 1994). Turbidity is another term that is
often used to describe water quality. Turbidity is measured by optical methods that
are often difficult to quantify accurately in terms of weight or volume of substances
present while suspended sediments are measured in physical terms to provide useful
weight and volume measurements for management purposes. Secchi measurements
also measure water clarity but as with turbidity measurements they are difficult to
quantify in terms of substances present. Since neither turbidity nor sec chi measurement can be accurately quantified, we have chosen to use suspended sediments in our
discussion. However, the concepts for remote sensing measurements of turbidity or
secchi depths would be similar. Suspended sediments increase the radiance emergent
from surface waters (Fig. 13.1) in the visible and near infrared proportion of the
electromagnetic spectrum (Ritchie et al. 1976). In situ and controlled laboratory
measurements have shown that surface water radiance is affected by sediment type,
texture, and color (Ho1yer 1978; Novo et al. 1989a; Han and Rundquist 1996), sensor
view and sun angles (Ritchie et al. 1975; Novo et al. 1989b; Ferrier 1995), and water
depth (Mantovani and Cabral1992).
Airborne platforms (Hilton 1984; Dekker et al. 1992, 1995) using photography
(Klooster and Schertz 1974), line scanners (Gite1son et al. 1991; Dekker et al. 1992),
multispectral scanners (Dekker et al. 1992) and video (Mause1 et al. 1991; Roberts
et al. 1995) have all been used to study suspended sediment patterns. Since the mid
1980s remote sensing studies of suspended sediments have been made using data
from satellite platforms such as Landsat (Kritikos 1974; Carpenter and Carpenter
1983; Khorram 1985; Ritchie et al. 1990; Harrington et al. 1992), SPOT (Lathrop and
Lillesand 1989; Froidefond et al. 1993), IRS (Choubeyand Subramanian 1992),
A VHRR (Strumpf and Pennock 1991; Froidefond et al. 1993), and CZCS (Coastal
Zone Color Scanner) (Amos and Toplis 1985; Mayo et al. 1993).
These studies have shown significant relationships between suspended sediments
and radiance or reflectance from spectral wave bands or combinations of wave bands
on satellite and aircraft sensors. Ritchie et al. (1976) using in situ studies concluded
291
13.4 Case Studies
Remote sensing applications to water quality are limited to measuring those substances or conditions that influence and change optical and/or thermal characteristics
of the apparent surface water properties. Suspended sediments, chlorophylls (algae),
DOM (humus), oil, and temperature are water quality indicators that can change the
spectral and thermal properties of surface waters and are most readily measured by
remote sensing techniques. Substances (i.e., chemical) that do not change the optical
and/or thermal characteristics of surface waters can only be inferred by modelling
using other surrogate properties (i.e., suspended sediments, chlorophylls) which may
have responded to an input or reduction of chemicals. Examples of applications of
remote sensing for measuring suspended sediments, chlorophylls, oils, and temperature will be given.
13.4.1 Suspended Sediments
Suspended sediments are the most common pollutant both in weight and volume in
surface waters of freshwater systems (Lal, 1994). Turbidity is another term that is
often used to describe water quality. Turbidity is measured by optical methods that
are often difficult to quantify accurately in terms of weight or volume of substances
present while suspended sediments are measured in physical terms to provide useful
weight and volume measurements for management purposes. Secchi measurements
also measure water clarity but as with turbidity measurements they are difficult to
quantify in terms of substances present. Since neither turbidity nor sec chi measurement can be accurately quantified, we have chosen to use suspended sediments in our
discussion. However, the concepts for remote sensing measurements of turbidity or
secchi depths would be similar. Suspended sediments increase the radiance emergent
from surface waters (Fig. 13.1) in the visible and near infrared proportion of the
electromagnetic spectrum (Ritchie et al. 1976). In situ and controlled laboratory
measurements have shown that surface water radiance is affected by sediment type,
texture, and color (Ho1yer 1978; Novo et al. 1989a; Han and Rundquist 1996), sensor
view and sun angles (Ritchie et al. 1975; Novo et al. 1989b; Ferrier 1995), and water
depth (Mantovani and Cabral1992).
Airborne platforms (Hilton 1984; Dekker et al. 1992, 1995) using photography
(Klooster and Schertz 1974), line scanners (Gite1son et al. 1991; Dekker et al. 1992),
multispectral scanners (Dekker et al. 1992) and video (Mause1 et al. 1991; Roberts
et al. 1995) have all been used to study suspended sediment patterns. Since the mid
1980s remote sensing studies of suspended sediments have been made using data
from satellite platforms such as Landsat (Kritikos 1974; Carpenter and Carpenter
1983; Khorram 1985; Ritchie et al. 1990; Harrington et al. 1992), SPOT (Lathrop and
Lillesand 1989; Froidefond et al. 1993), IRS (Choubeyand Subramanian 1992),
A VHRR (Strumpf and Pennock 1991; Froidefond et al. 1993), and CZCS (Coastal
Zone Color Scanner) (Amos and Toplis 1985; Mayo et al. 1993).
These studies have shown significant relationships between suspended sediments
and radiance or reflectance from spectral wave bands or combinations of wave bands
on satellite and aircraft sensors. Ritchie et al. (1976) using in situ studies concluded