524
C.B. Field et al.
soil moisture difficult to quantify, except in sites with very little vegetation
(Choudhury et al. 1987). Microwave reflectance in active, synthetic aperture
radar (SAR) systems is also sensitive to soil moisture, but only the longer
wavelengths penetrate to the soil. Detection of soil moisture with experimental SAR systems is a rapidly developing, promising area (Ustin et al.
1991). Passive microwave emissions can also be used for the remote sensing
of precipitation (Barrett 1991), offering an alternative approach to calculating
soil moisture.
24.6 Conclusions
Remote sensing of photosynthesis represents a variety of techniques applied
over a variety of scales. From the leaf to the global scale, however, the
methods provide information that is difficult or impossible to obtain with
other approaches, but that also tends to be difficult to interpret. The difficulty
of interpretation has been and must continue to be addressed on several
fronts. A clear physical understanding of the rediative transfer is important,
but it is also critical to recognize that the factors controlling a remote
sensing signature can be physical, biochemical, or ecological in nature. The
development of new remote sensing instruments and techniques will provide
improved access to some of these factors, but it is also important to continually rethink physiological and ecological models in the context of the
nature and quality of the remote sensing data. Extending small-scale techniques to large spatial scales involves a number of challenges that can only
be addressed with theoretical and empirical studies at a range of scales.
Remote sensing has led to important advances in the understanding of
photosynthesis, and it offers exciting prospects for the future. The advances
of the past have come from studies at a range of spatial scales and especially
from studies in which the analysis of remote sensing data is combined with
analysis of data from other sources. This paradigm provides a blueprint for
future progress.
Acknowledgments. This chapter is dedicated to Professor Otto Lange, whose pioneering
work in applying photosynthesis measurements to ecological questions laid many of
the foundations for the work described here. Thanks to NASA (EOS/IDS award) for
stimulating our studies in remote sensing and to awards from Fundaci6n Conde de
Barcelona and CICYT (Spain) for allowing JP to participate in them. Comments from J.
Randerson were very useful.
References
Adams JB, Smith MO, Johnson PE (1986) Spectral mixture modeling: a new analysis of
rock and soil types at the Viking Lander I Site. J Geophys Res 91: 8098-8112
C.B. Field et al.
soil moisture difficult to quantify, except in sites with very little vegetation
(Choudhury et al. 1987). Microwave reflectance in active, synthetic aperture
radar (SAR) systems is also sensitive to soil moisture, but only the longer
wavelengths penetrate to the soil. Detection of soil moisture with experimental SAR systems is a rapidly developing, promising area (Ustin et al.
1991). Passive microwave emissions can also be used for the remote sensing
of precipitation (Barrett 1991), offering an alternative approach to calculating
soil moisture.
24.6 Conclusions
Remote sensing of photosynthesis represents a variety of techniques applied
over a variety of scales. From the leaf to the global scale, however, the
methods provide information that is difficult or impossible to obtain with
other approaches, but that also tends to be difficult to interpret. The difficulty
of interpretation has been and must continue to be addressed on several
fronts. A clear physical understanding of the rediative transfer is important,
but it is also critical to recognize that the factors controlling a remote
sensing signature can be physical, biochemical, or ecological in nature. The
development of new remote sensing instruments and techniques will provide
improved access to some of these factors, but it is also important to continually rethink physiological and ecological models in the context of the
nature and quality of the remote sensing data. Extending small-scale techniques to large spatial scales involves a number of challenges that can only
be addressed with theoretical and empirical studies at a range of scales.
Remote sensing has led to important advances in the understanding of
photosynthesis, and it offers exciting prospects for the future. The advances
of the past have come from studies at a range of spatial scales and especially
from studies in which the analysis of remote sensing data is combined with
analysis of data from other sources. This paradigm provides a blueprint for
future progress.
Acknowledgments. This chapter is dedicated to Professor Otto Lange, whose pioneering
work in applying photosynthesis measurements to ecological questions laid many of
the foundations for the work described here. Thanks to NASA (EOS/IDS award) for
stimulating our studies in remote sensing and to awards from Fundaci6n Conde de
Barcelona and CICYT (Spain) for allowing JP to participate in them. Comments from J.
Randerson were very useful.
References
Adams JB, Smith MO, Johnson PE (1986) Spectral mixture modeling: a new analysis of
rock and soil types at the Viking Lander I Site. J Geophys Res 91: 8098-8112