• Drone helps researchers find fresh water

    From ScienceDaily@1:317/3 to All on Tue Sep 21 21:30:38 2021
    Drone helps researchers find fresh water in the sea at Easter Island


    Date:
    September 21, 2021
    Source:
    Binghamton University
    Summary:
    Researchers have demonstrated the effectiveness of using drones
    to locate freshwater sources at Easter Island.



    FULL STORY ========================================================================== Researchers at Binghamton University, State University of New York have demonstrated the effectiveness of using drones to locate freshwater
    sources at Easter Island.


    ==========================================================================
    The people of Easter Island appeared to drink directly from the sea,
    European explorers reported in the late 1700s. And today, you can see
    animals -- most famously horses -- do the same thing.

    What's going on? While surrounded by a vast ocean, fresh water is
    a scarce commodity on Rapa Nui, as the island is known to its native inhabitants. No rivers or streams cross its surface, and it sports only
    three small crater lakes that can dry up during periodic droughts.

    Due to a quirk of geology, rainwater immediately sinks down through
    the porous bedrock, where it feeds an underground aquifer, explained
    Binghamton University's Robert DiNapoli, a postdoctoral research associate
    in environmental studies and anthropology. That freshwater emerges at
    spots on the coastline known as coastal seeps.

    "At some of these locations on the shoreline, there is so much water
    coming out (from the seeps) that it's basically fresh. It's somewhat
    salty, but not unpalatably salty," DiNapoli said. "It's just not the best-tasting water, basically." DiNapoli, Professor of Anthropology and Environmental Studies Carl Lipo, Director of the Geophysics and Remote
    Sensing Laboratory Timothy De Smet and Terry Hunt of the University of
    Arizona recently demonstrated the effectiveness of thermal imaging drones
    in detecting the location of these coastal seeps. The results of their
    pilot project, "Thermal imaging shows submarine groundwater discharge
    plumes associated with ancient settlements on Rapa Nui (Easter Island,
    Chile)," was recently published in Remote Sensing.



    ==========================================================================
    It's not possible to use satellite imagery to identify freshwater sources
    on Rapa Nui because the pixel sizes are too large to register the coastal
    seeps in any detail, DiNapoli explained. A drone, on the other hand,
    flies at lower altitudes and can gather high-resolution images.

    Thermal imaging drones had previously been used in Hawai'i to investigate coastal seeps there. Lipo and DiNapoli, however, didn't know if this
    technology would work in Rapa Nui, where the freshwater plumes were much smaller in scale.

    As they discovered in their pilot project, it did.

    Before thermal imaging cameras, researchers literally needed to wade
    out into the water and measure the temperature and salinity by hand.

    "That's really labor-intensive because you need to walk and then every
    10 meters or so, you need to take a measurement," DiNapoli said.

    Not only is the drone system faster, but it provides a more substantial
    picture of the larger water feature, allowing researchers to see its characteristics as a whole. There is a downside, however: the heat
    reflecting off metal roofs and a local bonfire skewed the temperature
    readings on one of the flights.



    ========================================================================== Certain objects have characteristics that confuse the thermal camera,
    and thus their actual temperature isn't recorded, DiNapoli explained. A
    metal roof in the sun, for example, tends to be quite hot, but the
    thermal cameras register it as cold because of the reflected radiation.

    When the drone takes off, it begins calibrating and determining the
    area's high and low temperatures. Anomalies such as fires throw off
    that calibration.

    "It still gets us usable images in the sense that you can see relative differences in temperature, but the absolute temperature it's giving
    us is wildly off, so it says things are much colder or much hotter than
    they actually are," he said.

    Strategies for survival In their research, Lipo and DiNapoli explore
    the way that ancient communities used these seeps, on an island where
    droughts are common.

    In addition to collecting rainwater, the Rapa Nui people also constructed basin-type wells called puna that intercept the stream from the aquifer
    before it reaches the sea. They also built underwater dams in the ocean to prevent the seawater from mixing with the fresh water at the seep sites, although these structures have long since crumbled away.

    "It again provides an interesting example of how the people there were responding to the constraints of the island," DiNapoli said. "They
    were faced with a very difficult place to live and they came up with
    these interesting strategies for survival." As the first European
    visitors noted, the people also drank directly from the ocean at the
    seeps. The island's current inhabitants still pump water directly from
    these freshwater spots in the sea and use it to water crops and provide
    water for their livestock.

    In their previous research, Lipo and DiNapoli noted that Easter Island's
    famous archaeological features, such as the moaiplatforms, correlate
    closely to the location of freshwater resources.

    "This is where they're doing their ceremonial activities, this is where
    they're building their villages," DiNapoli said.

    Nor did topography prove a significant obstacle to the resilient
    islanders.

    Rapa Nui's western side is rimmed by steep cliffs, which would have made
    it difficult for people to access the shoreline seeps. Archaeological
    evidence and analyses of human bones in this area suggests, however,
    that people were making it down to the sea at these sites. In the paper, DiNapoli and Lipo investigated an area called Te Peu where coastal seeps
    are located directly adjacent to an ancient village.

    Further research The study's results are the jumping off point for
    another research project, funded by a National Geographic grant,
    to identify the location of coastal seeps throughout the island. The
    thermal imaging drone will play a major role in collecting the data.

    One of the questions they hope to answer is how coastal seeps respond
    to lengthy droughts. During their last research trip, the island was experiencing a multi-year dry spell, which dried up two of the crater
    lakes and sunk the third to low levels.

    "But we identified these coastal seeps all around the island. That
    suggests that when the island experiences these drought events, the seeps
    are one of the last water sources to be affected by it," DiNapoli said.

    One potential explanation: When the water goes underground after heavy
    rain, it likely stays in the aquifer for several years before discharging
    into the ocean. In their upcoming field work, DiNapoli and Lipo will
    try to confirm this, and determine how long it takes rainwater to make
    its underground journey to the sea.

    "We don't know that for sure, but that's one potential explanation for
    why these seeps are more resilient," DiNapoli said.

    ========================================================================== Story Source: Materials provided by Binghamton_University. Original
    written by Jennifer Micale. Note: Content may be edited for style
    and length.


    ========================================================================== Journal Reference:
    1. Robert J. DiNapoli, Carl P. Lipo, Timothy S. de Smet, Terry L. Hunt.

    Thermal Imaging Shows Submarine Groundwater Discharge Plumes
    Associated with Ancient Settlements on Rapa Nui (Easter Island,
    Chile). Remote Sensing, 2021; 13 (13): 2531 DOI: 10.3390/rs13132531 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2021/09/210921091735.htm

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