44
Chapter 5
calibrated physical measurements and of a wealth of data processing
methodologies available to derive the information required. Additionally, in
addressing solutions to data to information conversion problems, it must
always be recognized that, in general, utilization of other sources of data and
information will be necessary in order to derive the necessary information
from remote sensing sources, and that remote sensing sources alone will not
satisfy all the requirements nor will they necessarily be the most cost
competitive.
4.2
Quantitative measurement
Once all these things are understood, an interesting question arises: “Are
we making the right measurements?” Our knowledge of the physics of the
process is now complete enough that a lack of answers to that question no
longer needs to be the case. At the present time, with the exception of
systems being developed to monitor global change, Earth Observation
satellites and sensors are launched (and many millions of dollars are spent)
without sufficient attention being paid to this question which is, or at least
should be, based on the economic and social impact the use of the systems
will have. The relationship between our ability to accurately derive
quantitative physical variables from the raw data and the value of the
ultimate information supplied has been pointed out in previous sections. At
the present time, with few exceptions, simultaneous acquisition of the
concentration of variable gases and aerosols in the atmosphere along with
the principal data does not occur and adequate DEM's do not exist (or are not
available) for most of the land surface of the world. We know how to acquire
these data. Ozone and water vapor have well known spectral characteristics
and algorithms exist to parameterize atmospheric models such as
MODTRAN and 6S using measurements made simultaneously with those of
the main instrument. The necessary measurements could be made with a
small companion instrument having a spatial resolution in the 100 - 300
meter range and 6 or 7 narrow spectral bands in the VNIR range. A DEM
could be acquired with a specialized mission flying a true SAR
interferometer such as the TOPSAT mission proposed a number of years
ago. There are no technological mysteries here.
4.3
Alternate sources of information
Viewed from the perspective of information requirements, space-based
sources of data are simply one source of the data required to produce
information. To be utilized in an operational way, these sources must be
competitive with alternative sources of data. In other words, they must be
Chapter 5
calibrated physical measurements and of a wealth of data processing
methodologies available to derive the information required. Additionally, in
addressing solutions to data to information conversion problems, it must
always be recognized that, in general, utilization of other sources of data and
information will be necessary in order to derive the necessary information
from remote sensing sources, and that remote sensing sources alone will not
satisfy all the requirements nor will they necessarily be the most cost
competitive.
4.2
Quantitative measurement
Once all these things are understood, an interesting question arises: “Are
we making the right measurements?” Our knowledge of the physics of the
process is now complete enough that a lack of answers to that question no
longer needs to be the case. At the present time, with the exception of
systems being developed to monitor global change, Earth Observation
satellites and sensors are launched (and many millions of dollars are spent)
without sufficient attention being paid to this question which is, or at least
should be, based on the economic and social impact the use of the systems
will have. The relationship between our ability to accurately derive
quantitative physical variables from the raw data and the value of the
ultimate information supplied has been pointed out in previous sections. At
the present time, with few exceptions, simultaneous acquisition of the
concentration of variable gases and aerosols in the atmosphere along with
the principal data does not occur and adequate DEM's do not exist (or are not
available) for most of the land surface of the world. We know how to acquire
these data. Ozone and water vapor have well known spectral characteristics
and algorithms exist to parameterize atmospheric models such as
MODTRAN and 6S using measurements made simultaneously with those of
the main instrument. The necessary measurements could be made with a
small companion instrument having a spatial resolution in the 100 - 300
meter range and 6 or 7 narrow spectral bands in the VNIR range. A DEM
could be acquired with a specialized mission flying a true SAR
interferometer such as the TOPSAT mission proposed a number of years
ago. There are no technological mysteries here.
4.3
Alternate sources of information
Viewed from the perspective of information requirements, space-based
sources of data are simply one source of the data required to produce
information. To be utilized in an operational way, these sources must be
competitive with alternative sources of data. In other words, they must be