216
West Africa had trees growing in salt water that could reach those heights – turns
out it is a combination of high rainfall, high temperatures, and a low frequency of
tropical storms.
We were able to figure out the height of these trees by using pictures collected
from space, and a few lasers too (but don’t worry, these lasers are safe). These pictures (Fig. 13.1) were generated by using specific properties of radar (think radio
waves), the forest canopy, and some mathematical equations that involve imaginary
numbers to calculate the volume of scatterers (think objects off which a signal can
bounce) within the forest. The vertical distribution of that volume can give us an
estimate of how tall the forest is. Just to be sure that our estimates are accurate, we
also use independent measurements from space-borne lasers to double check our
work. The GLAS instrument, a sophisticated set of lasers onboard the now defunct
Ice and Cloud Elevation Satellite (ICESat), can accurately and precisely measure
the travel time of each of those laser pulses. Depending upon where that laser pulse
hits the surface, for example the ground or the top of the canopy, we can then determine the height of the trees by subtracting those two values. However, unlike the
radar image that gives us a picture of the entire landscape, the laser data only gives
us information for discrete locations. But the benefit is that we have a bunch of these
individual points adding up to thousands of points across the world. By marrying
the data we get from the radar image with the individual points from the lasers we
can calibrate and validate our canopy height models – the errors we get are only a
few feet apart. And this brings me back to the reason why we are in Gabon, to triple
check our data and actually measure the height of trees in the field.
Two boats pull up to the dock. The rain is still coming down. Our team rushes to
load the pile of equipment and gear we are bringing on our trip. We are going to be
camping for 2 weeks in a remote village nestled within the mangrove forests, so
everything is coming with us; tents, sleeping bags, stove, food, notebooks, measuring tapes, maps, GPS, and the list goes on. We divide the gear and the people
between the two boats. We try to keep things dry, but it is futile in the downpour.
Our journey across the river starts soaked to the skin.
We arrive in the village, no more than ten homes scattered along a hillside.
Curious community members peer out from their wooden, tin-roofed homes to see
the visitors. By now, almost 2 h after we shipped out, the late afternoon sun peeks
out from behind the clouds. It has finally stopped raining. It is worth noting that
there is a language barrier. Gabon is a French-speaking country. And although the
US-based crew does know some romance languages, French is not one of the better
ones. Luckily, our team from the University know more broken-English than we
know broken-French. The captain beaches the boat along the banks and a few of us
jump out into shin-deep mud, foreshadowing the next 2 weeks, and walk up the hill
to meet the chef du village.
The chief welcomes us to the village and opens his home to a group of strangers.
We finish setting up camp as dusk approaches. There are tents scattered around the
house. Choice of location was first come, first served. The prized spots were the
back porch and the front porch which allowed for the most air circulation. A large
open room separated the two porches. The tent I brought with me was pitched in that
D. Lagomasino
West Africa had trees growing in salt water that could reach those heights – turns
out it is a combination of high rainfall, high temperatures, and a low frequency of
tropical storms.
We were able to figure out the height of these trees by using pictures collected
from space, and a few lasers too (but don’t worry, these lasers are safe). These pictures (Fig. 13.1) were generated by using specific properties of radar (think radio
waves), the forest canopy, and some mathematical equations that involve imaginary
numbers to calculate the volume of scatterers (think objects off which a signal can
bounce) within the forest. The vertical distribution of that volume can give us an
estimate of how tall the forest is. Just to be sure that our estimates are accurate, we
also use independent measurements from space-borne lasers to double check our
work. The GLAS instrument, a sophisticated set of lasers onboard the now defunct
Ice and Cloud Elevation Satellite (ICESat), can accurately and precisely measure
the travel time of each of those laser pulses. Depending upon where that laser pulse
hits the surface, for example the ground or the top of the canopy, we can then determine the height of the trees by subtracting those two values. However, unlike the
radar image that gives us a picture of the entire landscape, the laser data only gives
us information for discrete locations. But the benefit is that we have a bunch of these
individual points adding up to thousands of points across the world. By marrying
the data we get from the radar image with the individual points from the lasers we
can calibrate and validate our canopy height models – the errors we get are only a
few feet apart. And this brings me back to the reason why we are in Gabon, to triple
check our data and actually measure the height of trees in the field.
Two boats pull up to the dock. The rain is still coming down. Our team rushes to
load the pile of equipment and gear we are bringing on our trip. We are going to be
camping for 2 weeks in a remote village nestled within the mangrove forests, so
everything is coming with us; tents, sleeping bags, stove, food, notebooks, measuring tapes, maps, GPS, and the list goes on. We divide the gear and the people
between the two boats. We try to keep things dry, but it is futile in the downpour.
Our journey across the river starts soaked to the skin.
We arrive in the village, no more than ten homes scattered along a hillside.
Curious community members peer out from their wooden, tin-roofed homes to see
the visitors. By now, almost 2 h after we shipped out, the late afternoon sun peeks
out from behind the clouds. It has finally stopped raining. It is worth noting that
there is a language barrier. Gabon is a French-speaking country. And although the
US-based crew does know some romance languages, French is not one of the better
ones. Luckily, our team from the University know more broken-English than we
know broken-French. The captain beaches the boat along the banks and a few of us
jump out into shin-deep mud, foreshadowing the next 2 weeks, and walk up the hill
to meet the chef du village.
The chief welcomes us to the village and opens his home to a group of strangers.
We finish setting up camp as dusk approaches. There are tents scattered around the
house. Choice of location was first come, first served. The prized spots were the
back porch and the front porch which allowed for the most air circulation. A large
open room separated the two porches. The tent I brought with me was pitched in that
D. Lagomasino