Plastic LiDAR

LiDAR datasets allow us to work with digital facsimiles of the earth surface and its adornments (e.g., vegetation). It’s also possible to transform the digital models back into physical form. I have been trying this with my 3D printer.

Figure 1. 3D printed relief map of the Fred study site. Ellipse is the location of 10 study plots. This is a print of the digital terrain model, or bare earth model, based on the 2019 LiDAR data from Glacier Bay. Compare Figure 7 in this previous post. The print is built by adding successive horizontal layers of plastic and the visible layers are reliable elevation contours, in this case about five foot contours.
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LiDAR canopies

The new LiDAR dataset for Glacier Bay includes not only the “bare earth” digital terrain model but also the point cloud which can represent vegetation and other things the airplane-borne LiDAR bounced off first before it bounced off the ground. This “first returns” cloud can show the shape of the upper vegetation canopy and even distinct understory strata. I have been trying to determine if any useful information can be quantified from the point cloud and to use QGIS to make colorful 3D images of the canopy models.

Figure 1. LiDAR first returns at Site 1 (the youngest site, emerged from the retreating glacier in 1968). Colors code for the intensity of the returned LiDAR signal. White dots are five study plots. Areas coded orange (the highest intensity) are dominated by Dryas drummondii and are present on both till and outwash. Green splotches surrounded by Dryas are cottonwood trees and willow shrubs. Blue-green clumps of vegetation are Sitka alder (circles). Gray is unvegetated outwash gravel (some of which is also blue or green). Specks (tiny squares) are noise (erroneous LiDAR returns well above the ground).
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Bare Earth surface

In 2019 Glacier Bay National Park paid to have LIDAR mapping data collected for about a third of the park. Last summer the processed data were delivered and have now started to appear online for downloading. Most of the data are good quality (6.14 points/meter²) and the area around Park Headquarters and two areas of the outer coast (Pacific coast) are better quality (16.52 points/meter²).

Figure 1. The 1750 terminal moraine at Bartlett Cove. Glacial ice advanced from the upper left and the front ice margin stayed at this place for long enough (a decade?) to built the ridge of sand, gravel, and boulders extending diagonally across the image. Meltwater from the glacier escaped over the moraine and eroded a channel through it and the glacial deposits in front of it (lower left). The moraine was densely forested when Europeans first studied it, so this is the first time recent scientists have been able to see the geomorphic features clearly. This map was made by Richard Carstensen using ESRI’s ArcGIS Pro software ($700/year). The downloaded LIDAR data does not look like this until much attention has been applied.
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Have photo – will date

The Fred and Goose Cove study sites at Glacier Bay are only 4.2 km (2.7 miles) apart and the glacier exposed Goose Cove only about a decade earlier than Fred. The vegetation development at Goose Cove during the two decades after I established the plots (ca. 1990-2010) should be comparable to the most recent two decades of development at Fred (ca. 2000-2020). Precise comparisons require that I know how old the two sites are.

Figure 1. Oblique aerial photo of the Muir Glacier (left) and the stagnating mass of the McBride Glacier (right) in July, 1929. Goose Cove is free of ice and the study plots established in 1988 (yellow squares) are mostly free of ice. Station 3 is one of William O. Field’s photo stations. NSIDC Digital File ID: muir1929071801.
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Dating Fred

The second youngest of my 10 study sites at Glacier Bay is called Fred because there is a USGS benchmark there named Fred. Fred is dominated by alder. When the plots were established in 1988, there were no spruce and the average diameter of the cottonwood trees was 7 cm (2.8 inches). There were about five of these little cottonwood trees in each plot and 280 alder stems. There are 10 plots and we measured the diameter of all 2800+ stems.

Figure 1. The 1995 field crew in Mother Alder in plot 4 at Fred. This alder was substantially larger and older than any other in the plots and probably begat many of its neighbors. Left to right: Jim Speer, Gary Bolton, Andi Lloyd, Ginger Burley, Elise Pendall. Kodachrome, May 24, 1995.

The primary source I used to date Fred’s emergence from under the glacier was an aerial photo taken in 1948. The McBride remnant, a large extent of shrinking, stagnant ice, was 550 m away from the plots and I guessed that four years earlier the ice had probably covered the plots. I was probably off by a few years.

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Dating retreat

Three decades ago I started monitoring vegetation change in Glacier Bay National Park where glaciers have been retreating and exposing new land to colonization by plants. Each of the 10 sites I study was exposed at a different date over the last 250 years and it’s important to know that date for each site. It seems even more important now that I have so much data from the sites.

Figure 1. The view of Muir Inlet from 2000 feet above Muir Point on the shoulder of Mount Wright. Across the inlet are 10 tiny yellow squares where the Morse Creek study site is. We established those study plots near Morse Creek in 1988 without knowing exactly when the glacial ice had melted away there. Foreground: Left; H. Lentfer, Right; author. Kodachrome slide, August 1988.
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Indiana Bats and the Grotto of Doom

More than a year ago I took a hike along the Green Mountain Escarpment (Vermont) in search of an old mine. I had read in an old report that Indiana bats hibernated in a mine in the area, and that was enough of an excuse to go exploring. I watched a bear and two cubs for 15 minutes but never found a mine. It was a pleasant hike along old logging roads through private property. No one lived on the several properties I traversed, none of which was posted.

Figure 1. This six acre wetland is at the base of the steep, rocky slopes I was exploring for a mine. Although I found nothing on the slopes resembling a bat hibernaculum, this wetland looked like excellent foraging habitat for bats. Plants in bloom include Canada goldenrod, jewelweed, boneset, joe pye weed, and New England aster. September 11, 2020.
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More noise, fewer bats

After 12 nights of recording bat calls near an Indiana bat maternity roosting colony, we deployed the AudioMoths for a week at the vernal pool where we recorded bat calls in August. Instead of putting two AudioMoths at the vernal pool, we put one by the pool and two in the forest surrounding the pool. One of the forest AudioMoths recorded nothing (a battery was inserted backwards), so we got data from only one non-pool AudioMoth.

Figure 1. Vernal pool MLS619 (Bridport, VT) on September 23, 2021 at the end of a week of recording bat calls. There was no standing water in the pool but the liquid mud was 6 inches deep. This might be as low as the water level gets in the pool this year (it was dry and firm last October). There were a few inches of water in the pool at the beginning of the AudioMoth recording on September 16.
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Maternal roosting

Indiana bats live throughout the US Midwest and into New England. In winter they gather in a small number of caves where as many as 50,000 bats may hibernate together. This makes the population vulnerable to vandalism and since 1967 the Indiana bat has been on the US endangered species list. It was listed as Vermont’s first endangered species in 1972. Communal hibernation also makes bats vulnerable to the spread of white-nose syndrome and Indiana bat populations have declined moderately since the disease appeared in 2006.

Vermont is at the northeastern edge of the Indiana bat’s range where it has been observed foraging and raising young throughout the southern Champlain Valley. About 10 maternity roosting colonies where females raise their pups have been documented in Addison County. Female bats select forested sites with large trees and spend the day under loose bark with their single pups and forage at night for flying insects within two or three miles of the roosting trees.

Figure 1. A shagbark hickory tree (Carya ovata) near the site of a known maternity roosting colony of the Indiana bat in Addison County. Female bats and their pups spend the day under the loose bark on living and dead trees of this and other species.
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Sound data

Part of the Vermont Center for Ecosystem Studies Vernal Pool Monitoring Project includes audio recordings to document the first calls of frogs at the pools. This year they started using AudioMoths to make the recordings. AudioMoths are open-source data loggers with a low-power sleep mode, real-time clock, microSD card slot, MEMS microphone, and circuitry to support audio capture. AudioMoths can be configured to automatically save audio recordings on a custom schedule. The AudioMoth software and hardware are well thought out and the audio quality is very good (see audio file below). The AudioMoths were deployed at about 50 Vermont vernal pools in weather-tight cases (Figure 1) and recorded for a few short sessions every night for several weeks in the spring.

Figure 1. The AudioMoth in a weather-proof case deployed at vernal pool NEW370 (near East Middlebury) between March 13 and May 8, 2021. It was configured to record for 10 minutes four times every night and save the wav files to a microSD card. The white plastic and foam is a rain hat which kept the AudioMoth drier but might have amplified the sound of big rain drops hitting it. April 11, 2021.
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Unsound data

A water depth data logger has been running unattended at a vernal pool (MLS619) at Snake Mountain in Bridport since April 10. The water was a meter deep when I waded out then to change the batteries and swap the microSD card. I have not been in a hurry to do the swap again assuming that the longer I wait the less wet I will get doing it. But I didn’t know how long the batteries would power the logger. The previous record was 11+ weeks, although a similar logger has been running in my office for more than a year on the same batteries. That one only saves data when certain conditions are met but it has been waking up every 30 minutes and sensing its environment for almost 13 months. I decided 16 weeks would make a good record for field deployment at MLS619 and was pleased to find that data had been written to the microSD card once every 30 minutes during those 3.7 months.

There was a lot more water in vernal pool MLS619 on July 30 than I expected. The level was only 11 cm lower than it was on April 10 when I last serviced the logger. I was even more surprised to learn that the water temperature was only 2.5 °C warmer than it was in April. Photo by Ned.
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Blueberry and hemlock

Some “then and now” sliders in the last post about Glacier Bay suggested that blueberry and hemlock were spreading in the understory at two of the older study sites we visited last month. Below I am trying out another method of displaying these pairs of old (1990 or 1995) and new (last month) photos. Some new photo pairs from York Creek and Beartrack Cove have been added as well as pairs from a third site.

  • 1995, York Creek, Plot 9, SE-NE
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