415
10:00 am to 4:30 pm. At midlatitudes, the longest time window for sun elevation
angles greater than certain angles occurs around summer solstice, while around the
equator, it is around the equinox. Calculators for sun position can be found online,
such as from the National Oceanic and Atmospheric Administration (NOAA,
https://www.esrl.noaa.gov/gmd/grad/solcalc/).
15.3.3 Airborne Campaigns
This section covers flight planning and some aspects of reference data collection for
image processing. Remote sensing of plant biodiversity typically involves matching
ecological and spectral data collected on the ground to remotely sensed images. Key
aspects to match ground and remote sensing data include choosing vegetation plots
that match the spatial resolution of the imagery (i.e., plots that are representative for
at least one pixel) and collecting accurate coordinate information at a relevant precision for the remote sensor; this and more is covered in Sect. 15.2.3 and the beginning of Sect. 15.3.
15.3.3.1 Flight Planning
Flight planning for airborne imaging spectroscopy campaigns starts with deciding
on the best time window(s) for the flight(s). The ideal time depends on the research
question, but generally it is when the phenomena of interest are most pronounced.
For example, for modeling and mapping aboveground productivity, peak biomass
could be a good time for acquiring airborne images; for differentiating plant species, early or late growing season could be the times of year when certain species
are most distinctive; for modeling and mapping plant disease or plant stress, different symptoms could be expressed at specific times of the year.
Schedules for flight crews are usually tight; thus communicating ideal flight windows early (i.e., at least several months in advance) is important. It is also critical to
communicate flight windows to site administrators as soon as possible (see Sect.
15.2.2). On the one hand, it might be important to limit disturbance (e.g., trampling
or destructive sampling) at the site during the week(s) leading up to a flight and to
have no people and/or equipment on-site during the time of the overflight. On the
other hand, other research groups might be interested in data collection around the
time of the overflight. Ideally, airborne data are collected under clear sky conditions
and low humidity. It is good practice to take the typical weather conditions at the
site into account and plan flights at a time of year with generally good sky conditions, if possible.
Typically, the next steps of flight planning include determining the desired pixel
size and drawing the flight lines. The ideal pixel size depends, again, on the goal of
the study and the study system. Image pixels can be larger for modeling biomass
and chemical composition at the plant community level than for predicting
15 Spectral Field Campaigns: Planning and Data Collection
10:00 am to 4:30 pm. At midlatitudes, the longest time window for sun elevation
angles greater than certain angles occurs around summer solstice, while around the
equator, it is around the equinox. Calculators for sun position can be found online,
such as from the National Oceanic and Atmospheric Administration (NOAA,
https://www.esrl.noaa.gov/gmd/grad/solcalc/).
15.3.3 Airborne Campaigns
This section covers flight planning and some aspects of reference data collection for
image processing. Remote sensing of plant biodiversity typically involves matching
ecological and spectral data collected on the ground to remotely sensed images. Key
aspects to match ground and remote sensing data include choosing vegetation plots
that match the spatial resolution of the imagery (i.e., plots that are representative for
at least one pixel) and collecting accurate coordinate information at a relevant precision for the remote sensor; this and more is covered in Sect. 15.2.3 and the beginning of Sect. 15.3.
15.3.3.1 Flight Planning
Flight planning for airborne imaging spectroscopy campaigns starts with deciding
on the best time window(s) for the flight(s). The ideal time depends on the research
question, but generally it is when the phenomena of interest are most pronounced.
For example, for modeling and mapping aboveground productivity, peak biomass
could be a good time for acquiring airborne images; for differentiating plant species, early or late growing season could be the times of year when certain species
are most distinctive; for modeling and mapping plant disease or plant stress, different symptoms could be expressed at specific times of the year.
Schedules for flight crews are usually tight; thus communicating ideal flight windows early (i.e., at least several months in advance) is important. It is also critical to
communicate flight windows to site administrators as soon as possible (see Sect.
15.2.2). On the one hand, it might be important to limit disturbance (e.g., trampling
or destructive sampling) at the site during the week(s) leading up to a flight and to
have no people and/or equipment on-site during the time of the overflight. On the
other hand, other research groups might be interested in data collection around the
time of the overflight. Ideally, airborne data are collected under clear sky conditions
and low humidity. It is good practice to take the typical weather conditions at the
site into account and plan flights at a time of year with generally good sky conditions, if possible.
Typically, the next steps of flight planning include determining the desired pixel
size and drawing the flight lines. The ideal pixel size depends, again, on the goal of
the study and the study system. Image pixels can be larger for modeling biomass
and chemical composition at the plant community level than for predicting
15 Spectral Field Campaigns: Planning and Data Collection