Group for Earth Observation

No 83 - September 2024

This artistic rendition illustrates Space Shuttle Endeavour during the STS99 SRTM Mission
Image: NASA

GEO MANAGEMENT TEAM

Useful User Groups

General Information

Weather Satellite Reports
This group provided weekly reports, updates and news
on the operational aspects of weather satellites.

John Tellick,email:GEO Newsletter Editor

https://groups.io/g/weather-satellite-reports

Les Hamilton,

SatSignal
This end-user self help group is for users of David
Taylor’s Satellite Software Tools, including the orbit
predictor WXtrack, the file decoders GeoSatSignal and
SatSignal, the HRPT Reader program, the remapper
GroundMap, and the manager programs - MSG DataManager, GOES-ABI Manager, AVHRR Manager etc.

email: lesw.hamilton@gmail.com

Technical Consultant (Hardware)David Simmons
email:

Webmaster and Website Matters

https://groups.io/g/SatSignal

Vacancy

MSG-1
This forum provides a dedicated area for sharing
information about hardware and software for receiving
and processing EUMETCast data.

e-mail:Management TeamDavid Anderson

https://groups.io/g/MSG-1

Rob Denton
Nigel Evans: nigel.m0nde@gmail.com

GEO-Subscribers
This is the official group is for subscribers of the Groupfor Earth Observation (GEO), aimed at enthusiasts
wishing to exchange information relating to either GEO
or Earth Observation satellites.

Clive Finnis
Carol FinnisPeter GreenDavid Simmons

https://groups.io/g/GEO-Subscribers/

David Taylor: david-taylor@blueyonder.co.uk

Copy for the Newsletter

GEO Quarterly Back-issue Archive

The Editor is always delighted to receive material for
inclusion in the GEO Quarterly Newsletter. These canrelate to any aspect of Earth Imaging, especially• Technical articles concerning relevant hardware andsoftware• Construction projects• Weather satellite images• Reports on weather phenomena• Descriptions of readers’ satellite imaging stations• Activities from overseas readers• Letters to the Editor• Problems and Queries for our experts to answer

GEO Quarterly has been in continuous publication since2004, and all previous issues are available on-line as
PDF copies from:https://leshamilton.co.uk/GEO/archive.htm

Contributions should of course be original and besubmitted to the editor by e-mail not later than the
middle of the month preceding publication.
If your article submission contains embedded images
and diagrams, please note that you must also submit
copies of the original images as separate attachments:
these are essential for page make-up purposes.
Materials for publication should be sent to the editor,
Les Hamilton, at

There is also a searchable index to all titles fromprevious years, and this can be downloaded from:https://leshamilton.co.uk/soft/geoindex-setup.exe

lesw.hamilton@gmail.com

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Les Hamilton

A
A

Important Information Concerning GEO
s of July 25, 2024, GEO’s web pages disappeared from the internet. Additionally, the email
addresses of its Management Team are no longer valid.

s many readers will know, GEO was set up by the late Francis Bell, who oversaw the Group’s
activities, including maintaining its on-line presence. It appears that, with the winding up of
his estate, GEO’s on-line presence has lapsed.

NA
T

otwithstanding, the GEO Quarterly Newsletter page, which has for some time now been
hosted on my own web space, is unaffected at:https://leshamilton.co.uk/GEO/newsletter.htm

ny reader needing to contact me with material for the newsletter should now use the email
address listed below (because the old “geo-web” email address is now defunct).
lesw.hamilton@gmail.com

he cover image this issue is an artistic representation of Space Shuttle Endeavour during theSTS99 Shuttle Radar Topography Mission undertaken in early 2000. This eleven-day mission
was responsible for acquiring the digital elevation model of Earth which is responsible for all thehigh definition topographic mapping available today. Read about this on page 12.

Contents
Geological Wonderland in Alaska
NASA Earth Observatory
Dunes and Desert replace the Aral Sea
NASA Earth Observatory
Botswana’s Salt Pans
MODIS Web Image of the Day
Svalbard Melts
NASA Earth Observatory
Early Summer Colour in Hudson Bay
Modis Web Image of the Day
The SRTM Mission to Map the Elevation of Earth
NASA Earth Observatory
MadeiraEuropean Space Agency
Daytime Land Surface Temperture (June 2024)
MODIS Web Image of the Day
How Climate Is Changing Earth’s Rotation
NASA JPL
Clear Skies over Svalbard Archipelago
MODIS Web Image of the Day
Shrinking Mar Chiquita
MODIS Web Image of the Day
TahitiCopernicus Image of the Day
Exploring the Beauty of Lake Eyre
Copernicus Image of the Day
Northwest Passage
MODIS Web Image of the Day
Australia’s Snowy Mountains Coated in White
NASA Earth Observatory
Etesian Winds over the Aegean Sea
MODIS Web Image of the Day
Foxe Basin’s Scenic Sea Ice
NASA Earth Observatory
Blowing in the Patagonian Wind
NASA Earth Observatory
Ship Tracks over the Pacific
MODIS web Image of the Day
Landslide Dams the Chilcotin River
NASA Earth Observatory
Home Reef Volcano Grows
NASA Earth Observatory
Tristan da Cunha
NASA Earth Observatory
Niagara Falls between Canada and the USA
Copernicus Image of the Day
Snow gathers on the Southern AlpsNASA Earth Observatory
A crystal clear view of Øresund Bridge
Copernicus Image of the Day
Forest Fire in Madeira
Copernicus Image of the Day
Satellite Status		

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Geological Wonderland in Alaska
NASA Earth Observatory
Story by Adam Voiland

NASA Earth Observatory image by Wanmei Liang, using Landsat data from the U.S. Geological Survey.

From a geological perspective,
Adam’s Inlet in Alaska has undergone
major changes in the blink of an eye.
Just 130 years ago, the inlet wascovered by ice hundreds of meters
thick. Today, it is ice-free. The inlet,
which drains into the East Arm of
Glacier Bay, lies within Glacier Bay
National Park.
‘Since the end of the Little Ice
Age about 150 years ago, Glacier
Bay has seen deglaciation on ascale almost unseen anywhere
else on Earth,’ said Dan
Shugar, a University of Calgary
geomorphologist. ‘In Adam’s Inlet,
the retreat of the ice has exposeda remarkable landscape. Steepslopes, glacial rivers, ocean tides
and sediment are smashing
together to create a geologicalwonderland.’The OLI-2 (Operational Land
Imager-2) on Landsat 9 captured
this image of the area on August28, 2023. Several streams flow into
the inlet, including a large one thatdrains meltwater from the Casement
Glacier. It is one of several glaciersin the eastern part of the park thathas retreated by several kilometresin recent decades, partly because ofwarming air and water temperatures.
‘These rivers transport incredible
quantities of fine-grained
sediment,’ stated Shugar. ‘They
are braided, meaning they havelots of strands that interweave,and can change dramatically fromday to day over the melt season.’
They also dump large quantities ofsediment into the ocean, resulting
in striking offshore plumes andsometimes giving the water aturquoise color. This effect, seen in
the eastern part of the inlet, is causedby rock flour (fine-grained silt and clay
particles) suspended in the water,that absorb certain wavelengths oflight. Also notable is the alluvial fan
near the centre of the image. Thesefeatures form where sediment-ladenrivers drain from narrow, steep valleys
into broader plains.
‘When the gradient decreases,
the water moves less quickly andis less able to carry sediment,’

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Shugar explained. ‘The sedimentdrops out and creates thesebeautiful landforms.’
Southeast of the alluvial fan, debris
from a landslide has tumbled into a
braided stream that enters the inlet
from the south. The landslide occurredin 2020, delivering enough material totemporarily block the stream. It has
since carved a channel through thedebris.
While that event caused minimal
damage, landslides crashing into
inlets in this region have had serious
consequences. In nearby Lituya Bay,an earthquake in 1958 triggered alandslide that sent 90 million tonsof rock plunging into the inlet andgenerated tsunami waves thatinundated land up to an elevation of
524 metres)—higher than New York’s
Empire State Building.
That event, one of the largest known
examples of a landslide, generated
waves that flattened so muchsurrounding forest that the damage isstill visible in Landsat imagery today.

4Dunes and Desert Replace the Aral Sea
NASA Earth Observatory
Story by Cadan Cummings, Jacobs, JETS II Contract at NASA-JSC.

Astronaut photograph ISS070-E-4509 was acquired on October 17, 2023 - © NASA / JSC

An astronaut aboard the International Space
Station took this photograph of the Aral Sea while
in orbit over Kazakhstan. This ‘sea’ is actually an
endorheic lake, located along the Kazakhstan andUzbekistan border and fed by the Amu Darya and
Syr Darya rivers. For the past 60 years, the lake has
experienced a rapid decline in surface area due tothe diversion of its two inflowing rivers to irrigate
crops. At its greatest extent, the Aral Sea would havespanned almost the entirety of this photo.
The Aral Sea was previously the world’s fourthlargest lake by surface area. But since the 1960s,
it has decreased to approximately 10 percent of its
original area. Desertification is visible toward thesoutheast where the dried lake bed has transformed
into the Aralkum Desert. This region is one of thenewest deserts in the world and spans 62,000
square kilometres. Sand dunes, built by winds

blowing across the dry landscape, are visible in thebottom-centre of the image. In addition to dunes, therapid aridification of the Aral Sea has triggered sandand dust storms that impact local air quality.
In the local Turkic language, ‘aral’ translates to‘island’, an allusion to the Aral Sea’s past as an
expansive lake with over 1,100 islands. The BarsaKelmes Nature Reserve is situated on one of theseformer islands, between the remains of the North
Aral Sea and South Aral Sea. The reserve provides
habitat for hundreds of plant and animal species. As
part of a U.S. Agency for International Development
project to restore the local ecosystem and slow
aridification, black saxaul shrubs (Haloxylon
aphyllum) are being planted to help reestablish
populations of native plant and animal species.
These also mitigate the effects of dust storms byhelping hold the soil in place.

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Botswana’s Salt Pans
MODIS Web Image of the Day

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

This striking false-colour image of Botswana’s
Makgadikgadi Salt Pans was acquired on
May 31, 2024, by the Moderate Resolution Imaging
Spectroradiometer (MODIS) on NASA’s Terra satellite.
The image was acquired at the end of the wet
season, when rainwater had moistened the mineralcrusts and accumulated to create areas of open
water in this normally remorselessly arid region.

The Salar de Uyuni, found in Bolivia, is the largest
continuous salt pan on Earth and the Makgadikgadi
Salt Flats come in second as far as contiguous
mineral crusting. However, when the desert andsavanna that are interspersed between the individual
salt flats that make up the Makgadikgadi are taken
into account, Botswana’s salt flats cumulatively spana larger area.

This type of false-colour image highlights water,which is coloured in electric blue tones, with deeper
water looking darker blue and shallow water muchlighter. Dry mineral crust, which is highly reflective,
looks white while the same type of crust, moistenedby underlying water, is tinted blue. Vegetation
appears bright green and open land is tan.

The pans are the salty remains of ancient
Lake Makgadikgadi. Scientists estimate that thisinland sea once spanned anywhere from 80,000 to
275,000 square kilometres. The Okavango, Zambezi,
and Cuando rivers probably emptied into this lake
until tectonic shifts changed the elevation of thelandscape and a changing climate dried up the rains.
After millions of years of evaporation and shifting
landscape this expanse of mineral-crusted flats is allthat remains of that massive prehistoric lake.

This collection of salt flats covers roughly
30,000 square kilometres across northern Botswana,northeast of Africa’s Kalahari Desert.

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Enrico Gobbetti acquired this Metop B image on August 10, 2024 using the Satdump software

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Svalbard Melts
NASA Earth Observatory
Story by Emily Cassidy

The Svalbard archipelago’s ice
caps suffered extreme episodes ofmelting in summer 2024, broughton by exceptionally high airtemperatures.
Situated between mainland
Norway and the North Pole,
Svalbard is one of the fastestwarming places on the planet.
Over half of its land area iscovered with ice, composing
about six percent of the planet’s
glaciated area outside Greenlandand Antarctica.
In late July and early August
2024, temperatures hoveredaround 4°C above average forthis part of the Arctic Circle.
The warming took its toll on
Svalbard, home to some of Earth’s
northernmost glaciers, causing
snow and ice to rapidly melt.
The OLI (Operational Land Imager)
on Landsat 8 captured theseimages of Nordaustlandet—the
second largest island in thearchipelago—on August 9, as
water and sediment drained off
the coast and into the Arctic
Ocean. Sediment is most likely
causing the striking swirls of
colour in the water surrounding
the island. The melting of seasonal
snow, and an older, compressed
layer of snow called ‘firn’, left
some areas of glacial ice (lightblue) bare and exposed in theimages.

Nordaustlandet, the second largest island in the Svalbard archipelago
as imaged by Landsat 8 on August 9, 2024
NASA Earth Observatory images by Lauren Dauphin,using Landsat data from the U.S. Geological Survey

According to Xavier Fettweis, aclimatologist at the Universityof Liège, Svalbard’s ice caps
broke their all-time record fordaily surface melt on July 23,2024. Svalbard shed about 55
millimetres of water equivalentthat day, a rate five times greaterthan normal.
The exceptional melting continued
into August, corresponding with apersistent heat dome that baked
parts of Scandinavia’s Arctic.

This expanded view of the southern coastline of Nordaustlandet, emphasises
the swirls of colour in the Arctic Ocean caused by meltwater runoff

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Detail from the northern peninsulas of Nordaustlandet island
NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey

In Longyearbyen, Svalbard’s capital on the mainisland of Spitsbergen, temperatures reached 20.2°C
on August 11, its highest August temperature on
record and about 2.2°C above the previous monthly
record, according to meteorologist Daan van den
Broek.

Svalbard experienced its warmest summer onrecord in 2023, according to the Copernicus Stateof the Climate report. This report cited several
contributing factors for the warmth, including belowaverage sea ice cover and above-average sea surface
temperatures.

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9Early Summer Colour in Hudson Bay
MODIS Web Image of the Day

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

As spring gave way to early summer in late June 2024,
the waters of southern Hudson Bay resembled an artist’s
palette—awash with sepia, sienna, turquoise and jadeshades, and topped by splashes of titanium white.
The Moderate Resolution Imaging Spectroradiometer(MODIS) on NASA’s Terra satellite acquired this truecolour image of the multihued scene on June 23.
The conglomeration of colours is a result of natural
events surrounding spring thaw. Each winter, Hudson
Bay and all rivers flowing into it freeze over. Snow lies
heavily over the surrounding landscape of northeastern
Canada. As temperatures warm and sunlight lengthensin late spring, snow and ice begin to melt. Meltwater
carries sediment from the land into rivers as well as theBay. In turn, the rivers dump their sediment load into
Hudson Bay as well as creating currents that can stirsediment up from the Bay’s bottom. Sediment appears
muddy brown when near the surface but takes on green
and blue tones as it sinks below the surface.
In this image, sediment is clearly apparent on thewestern shore, around Akimiski Island, and in thesouthern tip of the Bay. Along the shoreline, a mudcoloured halo strongly suggests that the primary sourceof this sediment is most likely run-off from the land.
The very dark colour in the south probably comes
predominantly from the sediment spilled by several large
rivers. This colour swirls northward towards the centre of
the Bay, following currents. Patches of bright white in thenorth are remnant patches of winter’s sea ice.
Hudson Bay’s freeze-thaw cycle has remained fairly
constant over recent decades, with sea ice typicallymelting between June and August and freeze-up
beginning again in late October or November. Morerecently, the tendency has been for melting to begin
early and freeze-up to begin later, extending ice-freedays. This is bad news for polar bears, which dependon plentiful ice to successfully hunt for ringed seals
and other prey. When ice melts, the bears retreat toshore where food is scarce. They must fast or feed onwhatever meagre food can be found until ice returns.
Since bears burn about one kilogram per day while onland, too much time on shore can lead to stress andstarvation.

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10This image of spectacular convective clouds over the island of Sicily wascaptured by the NOAA 21 satellite on August 5, 2024
Image: NASA Worldview Snapshots (https://wvs.earthdata.nasa.gov)

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The SRTM Mission to Map the Elevation of Earth
NASA Earth Observatory
Story by James Riordon/NASA’s Earth Science News TeamNASA Earth Observatory image by Michala Garrison, using topographic data from the Shuttle Radar Topography
Mission (SRTM) and SRTM coverage boundary data from the United States Geological Survey (USGS)Kevin Kregel had his lucky fishing hat firmly in place,complete with an array of fishing tackle above the floppy
brim and a chinstrap cinched up tight. It was time to try the
fly-cast manoeuvre. Commander Kregel wasn’t out for trout
on a mountain stream. He was at the controls of the space
shuttle Endeavour. Instead of wielding a fly-fishing rod, heand the crew of the 97th shuttle mission were preparing towhip a slender, 60‑metre-long mast into place on day twoof their 11-day quest to create an unprecedented map ofEarth.
With one end of the mast mounted in the orbiter’s payload
bay and the other cantilevered out into space, the it wasa central part of the Shuttle Radar Topography Mission(SRTM). It was also the longest instrument ever flown
aboard a space shuttle. A detector at the end of the mastand another nestled inside the shuttle bay were readyto collect reflections from a radar beam aimed at the
Earth below. First, there was the matter of swinging thefragile mast around to precisely orient the instrument inorbit. Doing it with a detector as heavy as a grand piano
attached to its far end was going to be the tricky part.
Closing Mapping Gaps
Nearly a quarter century after the mission to map theworld, the SRTM’s data still yields results. Just this year,
it aided in wildfire forecasting for Iran’s Zagros Mountains,tracking soil erosion in South Africa, assessing flood riskon the coast of Brazil, and even determining how thelocations of power-generating wind turbines affect realestate values. Tens of thousands of research papers are
published every year that rely on SRTM maps for theseand other environmental safety studies.
Back when Endeavour launched on February 11, 2000,
much of Earth’s surface was a mystery, topographicallyspeaking. No-one knew the precise heights of many of theworld’s mountains or the depths of the valleys between
them. Where height information did exist, topographicalmaps varied in quality and scale from country to country.
The result was an incomplete patchwork of maps.
Prior to 2000, correcting these mapping deficiencies had
proven elusive. Most imaging satellites had a hard timeseeing through cloud cover, particularly over portions ofSouth America and Africa. It was expensive to fly mapping
instruments on planes crisscrossing remote regions, and insome cases countries denied access to airborne mapping
efforts due to political conflicts. Scientists and engineers
at NASA’s Jet Propulsion Laboratory set out to solve theproblems with an instrument that could see through clouds
and map much of the planet over the course of a single
space shuttle mission.
Their solution was the SRTM instrument that now hangs
from the ceiling in the Smithsonian National Air and Space
Museum’s Steven F Udvar-Hazy Center in Fairfax County,
Virginia. Only a fraction of its fragile mast extends from thegolden canister where it was stored for the trip to orbit andback. Fully deployed, the trusswork of slender rods would

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reach two-thirds the length of a football field. When packed
away, the entire thing collapsed like an accordion to fit in
the canister, which is a bit taller than the average adult.
The radar system at the heart of the SRTM instrument
had flown twice on Endeavour for prior mapping efforts.
During those missions, the instrument offered twodimensional views of the ground from orbit. By combining
data from different vantage points, NASA scientists
produced stereoscopic images that revealed stunning 3D
topographic views. But the need for multiple passes overthe locations slowed the process, and while clouds aretransparent to radar, changes in the atmosphere between
orbits limited the quality and accuracy of the resulting
maps. The missions primarily focused on areas of scientificinterest in South America, Africa, Europe, Asia, andOceania, covering about 10% of the planet’s surface oneach of the two flights.

Part of the boom trusswork supporting the SRTM
instrument while in orbit on February 16, 2000
Photo from the NASA image and video libraryWith a radar antenna mounted at the end of the SRTM
mast and another inside the shuttle bay, the new
instrument could continuously view Earth in 3D, ensuringthat atmospheric changes from one orbit to another wereno longer a problem. Because it could capture images ina single pass over any given area, the SRTM would be
able to scan large areas of the planet and reveal detailed
topography nearly ten times faster than its predecessor.
In total, the SRTM collected elevation data over 80% ofEarth’s landmass in a single flight, with coverage spanning
the areas shown in the maps at the top of page 12.
Fishing for Data
Were it not for the weightlessness in orbit, a thousandpound radar antenna would have been far too heavy forthe delicate mast to handle. But even in space, there’s still
the problem of inertia—the resistance that objects withmass exhibit to changes to their motion. That meant that
the SRTM mast was going to flex whenever the spacecraft
turned to place the instrument in position to map the planet
below. Despite its rigid design, the long mast would act likea spring, with the antenna wobbling at the end after any
shuttle manoeuvres.

The SRTM instrument pictured at the end of the boom
while in orbit on February 12, 2000
Photo from the NASA image and video library“It’s a very small angle wobble, less than a degree,”said Scott Hensley, a senior research scientist at
JPL who helped develop the SRTM instrument, “butit translates into big error.” The motion would haveamounted to inaccuracies on the order of as much as
300 meters in features on a topographical map.
The JPL design team had anticipated the flexing andinstalled a system of gas jets at the end of the mast
to counteract the wobble. “It was a really clever idea,”
Hensley said. “It worked for like a day and a half, andthen I think it froze, so it no longer ejected the gas.”
Fortunately, engineer Bill Layman had outlined a fly-casting
contingency plan in the event of a problem with the jets.
Which brings us to Kregel and his fishing hat.
Layman’s fly-cast manoeuvre mimicked the motions thatsport fishers use when casting with long, flexible fly-fishingrods. In order to rotate the SRTM mast into position,

Kevin Kregel (left) and Endeavour pilot Dominic Gorie pictured
during the SRTM mission
Photos from the NASA image and video library

Kregel and Endeavour pilot Dominic Gorie, pictured above,
first applied a short burst with the shuttle’s thrusters,comparable to the initial flick of a fly rod. This caused themast to bend backward slightly as the shuttle turned, andthen to rebound forward. When the mast straightened out,
a second burst of the thrusters speeded up the shuttle’s
rotation, mimicking the forward portion of a cast.

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The timing and strength of the thrusts were tuned toprevent further vibrations as the mast swung into place.
Reversing the thruster procedure brought everything to aquiet, vibration-free halt, with the radar system in position
to start mapping.
Unlike the frozen gas jets, the fly-cast manoeuvre reliedon the shuttle’s limited supply of thruster propellant.
That meant the technique had the potential to cut themission short. But Kregel and Gorie managed the fly-castmanoeuvre to reposition the SRTM on six occasions withenough efficiency to leave plenty of propellant to complete
the full mapping schedule. The deft piloting allowed the
shuttle team enough time to collect elevation data overmost of Earth’s landmass, between the southern tip ofGreenland and the southern tip of South America.
In 2000, the space shuttle Endeavour flew its final scientificmission upside down and backwards. With the bay doors
open toward Earth below, the instruments of the Shuttle
Radar Topography Mission (SRTM) scanned the planetwith cloud-penetrating radio signals. With one detector at
the end of a telescoping 60-metre mast and another in the
shuttle’s bay, SRTM offered an unprecedented 3D view ofEarth (image at right).
This was not the final time that Endeavour went to space:
there would be 11 more flights over the following decade,primarily dedicated to supporting the International Space
Station. A quarter century later, though, the SRTM flightstands out as one of Endeavour’s most significant scientificmissions in its 19 years of service.

This artistic rendition shows Endeavour in orbit with the SRTM
boom extended, while surveying Earth
Image from the NASA image and video library

The SRTM system recorded data on magnetic tapesthat resembled large video tapes. Because the scanningran 24 hours a day for the duration of the mission,
the Endeavour crew split into two teams, working
alternate shifts, to change tapes every half hour. In all,they gathered 12 terabytes of data on 320 tapes overnearly 10 days. After a few years of data processing,the U.S. Geological Survey (USGS) made the resulting
topographical maps publicly available for free in 2003.
Initially, the USGS distributed high-resolution maps of the
U.S. with each pixel representing an area 30 metres ona side, roughly twice the size of a basketball court. Mapsof the rest of the planet initially featured lower-resolution
pixels 90 metres across. In 2015, the USGS released
full-resolution maps for the entire globe. Finally, in 2020,
NASA produced a new topographical map, designated
NASADEM (NASA Digital Elevation Model),https://www.earthdata.nasa.gov/esds/
competitive-programs/measures/nasademcreated with SRTM data that had been reprocessed to
improve the height accuracy of features. It also included
data from other mapping missions to fill in holes in theearlier maps.
SRTM Benefits Science, Society, Economics, and theEnvironment
Elevation is crucial information for a spectrum of scientificstudies, including many that directly address the safety

Maps such as this combining rainfall information with elevation
maps, can assist in predicting potential landslide dangers
Landslide susceptibility map by Jesse Allen, using data provided
by Thomas Stanley and Dalia Kirschbaum (NASA/GSFC), andtopographic data from SRTM.

and livelihoods of people around the planet. In areas
susceptible to flooding and landslides, estimates suggestthat thousands of lives could be saved each year bycombining rainfall information with elevation maps topredict landslide dangers (pictured above). Among thedata’s social justice applications, SRTM-based maps areproving crucial to the placement of health services andclinics for people in areas of difficult terrain in Sub-SaharanAfrica.

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Landscape features in regionsof the world that are difficult toaccess would likely remain hidden
today if it weren’t for SRTM and
NASADEM. Recently, Landsat 8
images overlain over SRTM
elevation maps have revealed theextraordinary depths of the remote
Cotahuasi Canyon in Peru, as seenin the image at right.
In another example, shown at the
top of the following page, the same
technique exposed enormous
folded rock landscapes in Canada,
scoured clean by retreating glaciers
following the last ice age.
In the decades since the shuttle
mapping mission, SRTM data havehelped researchers identify active
fault lines that could be the sourceof earthquakes in Afghanistan,estimate mangrove loss in
Malaysia due to deforestation, andeven determine how the locationsof power-generating wind turbines
affect real estate values. Tens of
thousands of research papers
are published every year that rely
on SRTM maps for these andother environmental, economic,
agricultural, and public safety
studies.

Landsat 8 images overlaid over SRTM elevation maps have revealed theextraordinary depths of the remote Cotahuasi Canyon in Peru
Images by Joshua Stevens, using topographic data from SRTM andLandsat data from the U.S. Geological Survey.

Topographic Maps Continue to Achieve New Heights
Other space-based measurements
Space Station called GEDI (Global
have added to our knowledge of
Ecosystem Dynamics Investigation)
Earth’s topography since SRTM.
have collected trillions of precise laser
Satellite missions such as NASA’s
measurements that have improved the
ICESat (Ice, Cloud, and land Elevation accuracy of the maps. The European
Satellite), its successor ICESat-2, and Space Agency’s Copernicus program
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15

This scene, referenced on the previous page, shows how a Landsat 8 image has been overlain
over an SRTM elevation map to reveal enormous folded rock landscapes in Canada
Images by Joshua Stevens, using topographic data from SRTM and Landsat data from the
U.S. Geological Survey.

data to create even more datasets of Earth’s surface
heights. Improvements to space-based topographic maps
will continue with the launch of the NASA-ISRO Synthetic
Aperture Radar, which will provide new, more precise
measurements of Earth’s surface.

Bawden expects SRTM-derived maps to be an invaluable
resource until the end of the century and beyond.

“Although future mapping efforts may offer improved
views of Earth, the value of the SRTM data showsno signs of diminishing”, stated Gerald Bawden, whooversees the SRTM program at NASA Headquarters.

For Scott Hensley, the senior research scientist at NASA’s
Jet Propulsion Laboratory (JPL) who helped develop the
instrument, the SRTM effort is both professionally andpersonally significant.

“The magic of SRTM is that we clearly had a nearglobal snapshot,” he said.
“It took less than two weeks to collect, but it now
provides a baseline for everything from climatechange and geologic hazards to urban planning anddeforestation. This is a gold mine of information for
coming generations.”“I’ve worked on a lot of cool missions, but SRTM is
one of the highlights of my career at JPL,” Hensleysaid. “It’s one of the things that I’m really proud of
because of its scientific and public benefits. I knowthat I’ve contributed to the betterment of humankind
by working on this mission.”

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16

This NOAA 19 image was acquired by Enrico Gobbetti on August 4, 2024 using the Satdump software.
Satdump describes this version of the NOAA channel 2 stream as MSA. In reality, the software has
extracted the cloud data from the image and superimposed it over a NASA BlueMarble backdrop.

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17

Madeira
European Space Agency
The Copernicus Sentinel-2 mission captured a rare,
cloud-free image over the Portuguese archipelago ofMadeira in the North Atlantic Ocean.
Lying off the northwest coast of Africa, thearchipelago is an autonomous region of Portugal
and comprises two inhabited islands, Madeira, thelargest, Porto Santo (top right), and two uninhabitedgroups, the Desertas (partially visible at the bottom)
and the Selvagens (not pictured).
The islands of Madeira are volcanic in origin: they
are the tops of mountains that rise from the ocean
floor deep below. The Portuguese explorers named
them Madeira, which is Portuguese for wood,inspired by the dense forests that covered the islands
when they arrived.
The lush main island of Madeira is famous for its
rugged, green landscape and is home to uniqueendemic flora and fauna.

The four islands of the Madeira archipelago
Image contains modified Copernicus Sentinel data (2024),
processed by ESA

MadeiraImage contains modified Copernicus Sentinel data (2024), processed by ESA

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18

To protect this natural environment, two thirdsof the island are designated as national park. The
Madeira Natural Park includes the Laurisilva of
Madeira, a Unesco World Heritage site and thelargest surviving area of primary laurel forest.
This type of vegetation is now confined to the
Macaronesian Islands: the islands of Madeira, theAzores, the Canary Islands and Cabo Verde.
Funchal, Madeira’s capital, can be seen as a large,
light-brown area on the island’s southeast coast,on the lower slopes of mountains that rise to1200 metres. The runway of Madeira’s airport isvisible on the east coast. Madeira’s airport is one of
the most challenging in the world to approach, due
to its exposure to the strong winds blowing over theflat Atlantic surface and the mountainous terrain.

Funchal, the capital city of Madeira on the south coast

Porto Santo, shown below, features white, sandy
beaches along its south coast. Here, the island’s
main town, Vila de Porto Santo, can also be spotted,
with its airport visible just to the north. At each endof the island are hills. At 515 metres, Facho Peak, on
the east, is the highest.
The narrow Desertas Islands at the bottom arealso designated as a natural reserve. Uninhabitedby humans due to scarce and poor-quality water,
Desertas are home to numerous species of birds, aswell as the protected Mediterranean monk seal. The
islands are relatively barren with their reddish andbrown ground, a reminder of their volcanic origin.

Madera Airport on the east coast

The island of Porto Santo

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19Daytime Land Surface Temperture (June 2024)
MODIS Web Image of the Day

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

During the month of June 2024, the Moderate
Resolution Imaging Spectroradiometer(MODIS) on NASA’s Terra satellite acquired
data that was used to create this Land
Surface Temperature (daytime) image of
the Earth. Land surface temperature is ameasurement of how hot the top millimetreof the land is to the touch. It differs from airtemperature (the temperature given in weather
reports) because land heats and cools more
rapidly than air.
This image depicts land surface temperature.
The warmest temperatures are pale yellow,
while the coldest temperatures are dark blue.
Moderate temperatures are depicted in shadesof pink and purple. Black means ‘no data’ wasgathered and is typical of ocean surfaces inthis dataset.
June is summer in the Northern Hemisphere
and winter in the Southern Hemisphere. The
most frigid temperatures, not surprisingly,
are found in Antarctica, where it is deep
winter. This is evident by the white area atthe bottom of the image. The Arctic, found in
the far north (top) is also showing cool land
temperature.
A large swath of the centre of the Earth’s
land masses, however, is covered in yellows,

depicting temperatures in the 32-45°C range.
This includes the Western United States,
portions of northern South America, theSahara Desert and part of the Sahel in Africa
as well as the Horn of Africa, the Arabian
Peninsula, India, parts of China, Mongolia,
and Russia, and even the top end of Australia.
Western Madagascar is also showing highland surface temperatures despite its location
far south of the equator.
Of particular note is that the boreal forest andnorthern tundra regions of North American,
Russia, and Europe appear in red, suggesting
substantially warm land surface temperatures.
In some boreal regions, where the ground istypically in permafrost and stays frozen yearround, land surface temperature appears toapproach 27°C—quite warm for boreal forests
in June. One example which has been used
to illustrate summer temperatures in boreal
forests is Lahti, Finland.
The mean average temperature in June
between 1970 and 2000 in Lahti was 15°C,
according to an article published by NASA’s
Earth Observatory Earth Explorer site.
The article can be found at the following URL:
https://earthobservatory.nasa.gov/
biome/bioconiferous.php.

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20

NASA-Funded Studies Explain

How Climate Is Changing Earth’s Rotation
NASA JPL

The Arctic is captured in this2010 visualization using datafrom NASA’s Aqua satellite. A new
study quantifies how climaterelated processes, including themelting of ice sheets and glaciers,
are driving polar motion.
Researchers used more than
120 years of data to decipher
how melting ice, dwindling
groundwater, and rising seas are
nudging the planet’s spin axis andlengthening days.
Days on Earth are growing
slightly longer, and that changeis accelerating. The reason
is connected to the samemechanisms that also havecaused the planet’s axis tomeander by about 10 metres in
the past 120 years. The findings
come from two recent NASAfunded studies focused on how
the climate-related redistributionof ice and water has affected
Earth’s rotation.

Figure 1
The Arctic is captured in this 2010 visualization using data from NASA’s Aqua satellite. A
new study quantifies how climate-related processes, including the melting of ice sheetsand glaciers, are driving polar motion. Another study looks at how polar meltwater is
speeding the lengthening of Earth’s day.
Credit: NASA’s Scientific Visualization StudioThis redistribution occurs whenice sheets and glaciers melt morethan they grow from snowfall,
and when aquifers lose moregroundwater than precipitation
replenishes. These resulting
shifts in mass cause the planet
to wobble as it spins and its axis
to shift location—a phenomenon
called polar motion (figure 2). They
also cause Earth’s rotation toslow, measured by the lengtheningof the day. Both have beenrecorded since 1900.
Analysing polar motion across
12 decades, scientists attributed
nearly all of the periodic
oscillations in the axis’ position
to changes in groundwater, ice
sheets, glaciers, and sea levels.
According to a paper publishedrecently in Nature Geoscience,
the mass variations during the20th century mostly resulted fromnatural climate cycles.

Figure 2
This image is taken from an animation, exaggerated for clarity, illustrating how Earth’s
rotation wobbles as the location of its spin axis, shown in orange, moves away from its
geographic axis, which is shown in blue and represents the imaginary line between theplanet’s geographic North and South poles.
The full animation can be accessed from the original NASA report at: https://www.jpl.
nasa.gov/news/nasa-funded-studies-explain-how-climate-is-changing-earths-rotation
Credit: NASA’s Scientific Visualization Studio

The same researchers teamed on asubsequent study that focused on
day length. They found that, sincewww.geo-web.org.uk

2000, days have been getting
longer by about 1.33 milliseconds
per 100 years, a faster pace than21

at any point in the prior century. The cause: theaccelerated melting of glaciers and the Antarctic
and Greenland ice sheets due to human-caused
greenhouse emissions. Their results were publishedin the July 15 Proceedings of the National Academyof Sciences.
‘The common thread between the two papers isthat climate-related changes on Earth’s surface,whether human-caused or not, are strong driversof the changes we’re seeing in the planet’s
rotation,’ said Surendra Adhikari, a co-authorof both papers and a geophysicist at NASA’s Jet
Propulsion Laboratory in Southern California.
Decades of Polar Motion
In the earliest days, scientists tracked polar motion
by measuring the apparent movement of stars. Theylater switched to very long baseline interferometry,
which analyses radio signals from quasars, orsatellite laser ranging, which points lasers at
satellites.
Researchers have long surmised that polar motion
results from a combination of processes in Earth’s
interior and at the surface. Less clear was how mucheach process shifts the axis and what kind of effecteach exerts—whether cyclical movements that repeat
in periods from weeks to decades, or sustained drift
over the course of centuries or millennia.
Need Some Space?
For their paper, researchers used machine-learningalgorithms to dissect the 120-year record. They
found that 90% of recurring fluctuations between
1900 and 2018 could be explained by changes ingroundwater, ice sheets, glaciers, and sea level.
The remainder mostly resulted from Earth’s interior
dynamics, like the wobble from the tilt of the innercore with respect to the bulk of the planet.
The patterns of polar motion linked to surface
mass shifts repeated a few times about every
25 years during the 20th century, suggesting to
the researchers that they were largely due tonatural climate variations. Past papers have drawn
connections between more recent polar motion andhuman activities, including one authored by Adhikarithat attributed a sudden eastward drift of the axis
(starting around 2000) to faster melting of theGreenland and Antarctic ice sheets and groundwater
depletion in Eurasia.
That research focused on the past two decades,
during which groundwater and ice mass loss as well
as sea level rise—all measured via satellites—have
had strong connections to human-caused climatechange.
‘It’s true to a certain degree’ that humanactivities factor into polar motion, said Mostafa
Kiani Shahvandi, lead author of both papers
and a doctoral student at the Swiss university

ETH Zurich. ‘But there are natural modes in
the climate system that have the main effect onpolar motion oscillations.’
Longer Days
For the second paper, the authors used satellite
observations of mass change from the GRACE
mission (short for Gravity Recovery and Climate
Experiment) and its follow-on GRACE-FO, as wellas previous mass-balance studies that analysed thecontributions of changes in groundwater, ice sheets,and glaciers to sea level rise in the 20th century toreconstruct changes in the length of days due tothose factors from 1900 to 2018.
Scientists have known through historical eclipse
records that length of day has been increasing formillennia. While almost imperceptible to humans,
the lag must be accounted for because many
modern technologies, including GPS, rely on precise
timekeeping.
In recent decades, the faster melting of ice sheets
has shifted mass from the poles toward theequatorial ocean. This flattening causes Earth todecelerate and the day to lengthen, similar to whenan ice skater lowers and spreads their arms to slow
a spin.
The authors noticed an uptick just after 2000 in
how fast the day was lengthening, a change closely
correlated with independent observations of theflattening. For the period from 2000 to 2018, the rateof length-of-day increase due to movement of ice andgroundwater was 1.33 milliseconds per century—
faster than at any period in the prior 100 years,
when it varied from 0.3 to 1.0 millisecond per
century.
The lengthening due to ice and groundwater changes
could decelerate by 2100 under a climate scenario
of severely reduced emissions, the researchers note.
(Even if emissions were to stop today, previously
released gases—particularly carbon dioxide—would
linger for decades longer.)If emissions continue to rise, lengthening of
day from climate change could reach as high as
2.62 milliseconds per century, overtaking theeffect of the Moon’s pull on tides, which has been
increasing Earth’s length of day by 2.4 milliseconds
per century, on average. Called lunar tidal friction,
this effect has been the primary cause of Earth’s
day-length increase for billions for years.
‘In barely 100 years, human beings havealtered the climate system to such a degree that
we’re seeing the impact on the very way theplanet spins,’ Adhikari said.
Reference URL for the Original Article
https://www.jpl.nasa.gov/news/
nasa-funded-studies-explain-how-climate-is-changing-earthsrotation

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22

This Meteor M2-3 RGB123 HRPT image was acquired by Enrico Gobbetti on July 2, 2024 using the Satdump software.

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23

Clear Skies over Svalbard Archipelago
MODIS Web Image of the Day

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

Beautifully clear skies allowed the Moderate Resolution
Imaging Spectroradiometer (MODIS) on NASA’s Terrasatellite to acquire a gorgeous true-colour image of the
Svalbard Archipelago on July 17, 2024.
This group of ice-coated islands, which belongs to Norway,
sits north of mainland Europe and halfway between
Norway and the North Pole. It is surrounded by the Arctic
Ocean (north), Barents Sea (southeast), Greenland Sea(southwest), and the Norwegian Sea. There are nine mainislands, including Spitsenbergen, which is the largest,

as well as North East Land, Edge Island, Barents Island,
Prins Karls Foreland, Kvit Island, Kong Karls Land, Bjorn(Bear) Island and Hopen.
In this image, sea ice covers the Arctic Ocean and snow
and ice sit atop most of the landmass. Some clouds arevisible in the south, and it appears that some fog (lowcloud) covers valleys in central Spitsbergen. Ice remains
atop Svalbard’s islands year-round, although sea ice
cover was exceptionally low in the summer of 2023 due tounusually high air temperatures.

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24

Shrinking Mar Chiquita
MODIS Web Image of the Day

Mar Chiquita imaged on July 16, 2000

Mar Chiquita imaged on July 13, 2024

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

The beautiful yet saline Mar Chiquita sits in central
Argentina, providing water to residents as well as
critical habitat for several types of bird. Mar Chiquita
has captured the title of Argentina’s biggest lake,
despite the fact the water level is variable. When thewater level is high, the lake covers as much as 6,000
square kilometres. When low, it shrinks to 2,000
square kilometres, exposing expansive salt and mud
flats along its northern shore.
The fluctuating water level can spur drastic changes
in salinity, with salt content ranging from 25 grams
per litre when the lake is brimming full, to 290
grams per litre when it shrinks. For comparison, sea
water typically contains about 35 grams per litre ofsalt.
Much of Argentina has been in significant drought
since at least 2022. This drove crop yields
dramatically down in 2023, especially in theprovince of Cordoba, where Mar Chiquita is located.
Lack of rainfall combined with high temperaturesand increased water diversion for human use
has resulted in dramatic shrinkage of the lake.
And several equally dramatic impacts. With more
mud flats exposed, the northern edge of the lakehas become a source of dust storms. Increasing
salinity and smaller area has raised concerns about
the ability of the lake to support the breeding ofChilean Flamingos. In addition, half of the world’s
population of Wilson’s Phalarope rests and feeds in
Mar Chiquita each year. Biologists are concernedthat shrinking saline lakes may tip some species into
severe crisis.
The Moderate Resolution Imaging Spectroradiometer(MODIS) on NASA’s Terra satellite acquired a pairof false-colour images that, when compared, show

the startling shrinkage of this biologically importantlake. The right-hand image was acquired on July 13,
2024, after light rains had slightly lightened at least
three years of drought. The left-hand image was
acquired more than two decades ago, on July 16,
2000, when Mar Chiquita was much more robust.
Water appears blue in this type of false-colour image,but deeper water looks deep blue while shallow water
has a light blue tint. Minerals and salts are highlyreflective and show up white: however, if they aredamp the presence of water adds a light blue shade.
Vegetation appears bright green while open or lightly
vegetated land looks tan or brown.

TahitiIn this crystal clear, true colour image taken by Copernicus
Sentinel-2 on 25 July 2024, depicts Tahiti and its precious
coral reefs. Earlier this summer, the village of Teahupo’o,known for its surf break and large waves, hosted thesurfing competitions of the Olympic Games 2024.
Credit: European Union, Copernicus Sentinel-2

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25

Exploring the Beauty of Lake Eyre
Copernicus Image of the Day

Credit: European Union, Copernicus Sentinel-2

Lake Eyre, officially known as Kati Thanda–Lake
Eyre, is an endorheic lake in the east-central
part of the Far North region of South Australia,around 700 kilometres north of Adelaide.
While the lake is mainly dry, with heavy rains
and the right con­di­tions, the lake comes to lifeand becomes home to thousands of water­birds

includ­ing pel­i­cans, sil­ver gulls, red-necked avo­
cets and more.
On July 20, 2024, Copernicus Sentinel-2
captured the full size of the lake. This scene is a
short-wave infrared composite. We can discern
vegetation in green, water in deep blue and dry
salt surfaces in turquoise.

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26

Northwest Passage
MODIS Web Image of the Day

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

The Northwest Passage traces a sea route from Europe
to Asia that winds through islands along the northernedge of Canada—a route much shorter than a trip aroundthe southern tip of Africa. While such a passage was alonged-for dream as far back as the second century CE, it
wasn’t until 1906 that the first recorded successful voyage
through the Northwest Passage was completed. It took
Roald Amundsen and his crew of six three years to sail his
21 × 6 metre sloop, a converted herring boat named Gjøa,
through the icy passage.
As the climate warms, the passage across the top of
Canada becomes more of a reality. Summer Arctic sea
ice minimum extent reached a new low in 2007, creating
conditions that fostered more frequent success formariners attempting the crossing. The summer Arctic sea
ice minimum reached a new record low in 2012. And,according to the NASA Climate website, summer Arctic
sea ice extent is shrinking by 12.2% per decade due
to warmer temperatures. Traffic through the Northwest
Passage now occurs on a regular basis during the peak ofsummer.
There is a twist to the story, however. According to
YaleClimate 360, melting sea ice appears to be making

the Northwest Passage more difficult. As ice nearer the
North Pole melts, it releases chunks of ice large enough toprove dangerous to ships. And these chunks are floating
down to the waters around northern Canada. They cite anarticle published in the journal Communications Earth andEnvironment, which found that the navigable period in the
Eastern Beaufort Sea, at the eastern edge of the passage,
had shrunk from 27 weeks in 2007 to 13 weeks in 2021.
On July 13, 2024, the Northwest Passage appeared toremain firmly covered in ice, based on this false-colour
image captured by the Moderate Resolution Imaging
Spectroradiometer (MODIS) on NASA’s Aqua satellite. The
image centres on Victoria Island, the largest island visible.
The route across the passage requires skirting Victoria
Island either to its north or south.
This type of image uses a combination short-wave
infrared, near infrared, and visible light (MODIS bands
7-2-1) to help highlight snow and ice, both of which appear
bright electric blue. In contrast, open, ice-free, ocean water
looks deep blue. Vegetation is green, open land is tan, andclouds are usually white although high, cold clouds which
are filled with ice crystals may take on a tint of pale electric
blue.

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27

Australia’s Snowy Mountains Coated in White
NASA Earth Observatory
Story by Lindsey Doermann

Winter made a bold—if late—entrance to the mountains insoutheastern Australia. Muchto the delight of skiers Down
Under, a period of seasonal
weather in July 2024 broughtsignificant accumulations to
the Snowy Mountains in New
South Wales.
The OLI (Operational Land
Imager) on Landsat 8 captured
this wintry image of Australia’s
Snowy Mountains on July 28.
Part of the Australian Alps, therange is home to the country’s
tallest peaks, including Mount
Kosciuszko at 2,228 metres,
as well as several popular ski
resorts. Peak snow season inthis region usually lasts from
June to August, althoughsnow commonly falls at higher
elevations in May and canlinger through October.
Winter got off to a slow start in
the Snowy Mountains in 2024,
however. Slopes were mostly
bare for the traditional openingof the ski season in early June,
according to news reports.
Meteorologists attributed
the lack of snow to blocking
highs, or strong high pressure
systems, that persisted overthe Great Australian Bight.
Weather patterns changedon July 19 as heavy snow
reached the mountains. On
July 21, the Thredbo ski resort
reported that 59 centimetersof snow had fallen during thestorm. Smaller accumulations
arrived in subsequent days.
Starting July 28, a strong cold
front delivered ‘unusually low’temperatures to parts of New
South Wales and yet moresnow fell on the mountains.
According to news reports,some of Australia’s extreme
winter weather in 2024 was
influenced by a rare sudden

NASA Earth Observatory image by Michala Garrison,using Landsat data from the U.S. Geological Survey

stratospheric warming event
over the Antarctic.
Variable snow years are thenorm in the Australian Alps,
according to the Australian
Bureau of Meteorology.
Climate patterns such as
El Niño, La Niña, and theIndian Ocean Dipole modulate
each winter’s snowpack.
Despite the significant year-

www.geo-web.org.uk

to-year variability, longterm observations point to athinning alpine snowpack.
Maximum snow depth hastrended down since the late
1950s, the agency reported,
adding that the declines
are linked with warming
trends. The annual averagetemperature has risen about
1.4 degrees Celsius in theregion since 1950.

28

Etesian Winds over the Aegean Sea
MODIS Web Image of the Day

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

Each summer, the Aegean Sea is combed by strong
northerly winds. Known as ‘Etesian winds’, they usuallyoriginate from air masses over southern Russia or
the Caspian Sea and sweep southward. They winds
are dry and relatively cool, so they can help moderate
the peak summer heat of Greece, Türkiye, and theassociated islands in the Aegean.
Etesian winds may come on suddenly and often reachgale force. Blowing between 62-74 kilometres per hour,gale‑force winds can cause difficulty with small craft
navigation and may feed rapid spread of wildfires.
The name ‘Etesian’ is said to derived from the Greek
word ‘etesios’, which means annual. They are also
known as ‘meltemia’ in the region.
On July 28, 2024, the Moderate Resolution Imaging
Spectroradiometer (MODIS) on NASA’s Terra satellite
captured a true-colour image that revealed thepresence of Etesian winds blowing across the Aegean

Sea. For orientation, Greece is in the west (left) andTürkiye sits in the east (right). Crete, a large Greek
island, stretches across the southern section of theimage at the border between the Aegean Sea (north)and Mediterranean Sea (south).
While the wind itself is, of course, invisible, the opticalphenomenon known as ‘sunglint’ marks its passage.
Sunglint occurs when the reflection of light off wateraims directly back at the satellite sensor. This createsa bright, mirror-like area in a true-colour image when
the water surface is still and flat. In contrast, where thesurface has been roughened by passing wind, lightis scattered in many directions, causing those areas
to appear darker. As flowing air strikes tall objects,
such as the tall terrain of Crete, it is blown around theobject. This creates turbulence near and on the edges,
but the lee side is protected from the wind and looks
bright. The direction of moving air can be estimatedfrom the patches of bright sunglint behind the islands,
including Crete.

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29

Foxe Basin’s Scenic Sea Ice
NASA Earth Observatory
Story by Kathryn Hansen

The seasonal melting of sea ice
across the central Arctic Oceanand surrounding basins peaks
in July, the region’s warmest
month. In Foxe Basin, currents,
tidal motion, and winds can stir
up the now-fragile pieces of ice,
producing art-like patterns on
the water’s surface. One such
moment of seasonal beauty wason full display on July 15, 2024,
when the OLI-2 (Operational Land
Imager-2) on Landsat 9 captured
the image shown in figure 1.
Foxe Basin, off the west coast of
Baffin Island in Nunavut, Canada,measures about 400 kilometersacross at its widest point. Hudson
Bay lies to the south, connected
Figure 1 - Foxe Basinto the basin by Foxe Channel, and
NASA
Earth
Observatory
imagesby Wanmei Liang using Landsat data from the USGS
additional waterways within the
Canadian Arctic Archipelago lie to the west. Figure 1
shows the northeastern part of Foxe Basin andseveral of its largest islands.
The basin’s waters are often clogged with first-year
sea ice—seasonal ice that is less than a year old.
New ice begins to form each year around October,according to Environment and Climate Change
Canada, and it continues to spread and thicken
through the winter until melting begins in late May
or early June. As of August 2024, the basin was
nearly ice-free, except for areas west of Baffin Island
and within Foxe Channel.
Figures 2 and 3 show detailed views of patterns
in the ice on July 15. The basin’s ice is often inmotion, producing the wispy tendrils of ice andpaths of open water that trail some of the larger
pieces.

Figure 2
A zoomed view at the eastern coastline of Foxe Basin

All of this motion also helps stir up sediment, whichis the main reason for the ice’s muddy appearance.
Pieces of eroded soil and debris—sloughed from thesurrounding land and stirred up from the shallow
seafloor—mix with the seawater and stain the icebrown. Algae, which can grow under the ice andwash on to its surface, might also be contributing to
the discoloration.
The basin is a haven for an array of wildlife. Several
polynas—areas of open water within the sea ice—are
an important gathering place for species such as
bowhead whales and polar bears. Walrus, migrating
birds, and other creatures also rely on the basin’s
resources.

Figure 3
Patterns in the ice to the south of Foxe Basinwww.geo-web.org.uk

30

Blowing in the Patagonian Wind
NASA Earth Observatory
Story by Adam Voiland

NASA Earth Observatory image by Wanmei Liang, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview

Strong northwesterly winds often race down theeastern side of the Andes Mountains and whip
across the central Patagonian Desert. In the process,they sometimes lift dust from Argentina’s drying
Lago Colhué Huapi, fuelling intense dust storms.
The MODIS (Moderate Resolution Imaging
Spectroradiometer) on NASA’s Aqua satelliteacquired this natural-colour image of dust streamingfrom the silty lake bed, east of Lago Musters, on
March 29, 2024. Lago Colhué Huapi
https://earthobservatory.nasa.gov/images/
148381/a-dusty-day-in-patagonia
is a particularly rich source of dust because theshallow lake regularly grows and shrinks withvariations in the flow of the Senguer River and thepace of evaporation. When lake water levels are low,
as they were when MODIS captured this image, finegrained, lightweight particles are easily transportedby the wind.
To better understand dust activity from Lago Colhué
Huapi, NASA scientists have analysed satellite andsurface weather data over five decades, assessing theyear-to-year variability in dust storms and identifying
periods of high activity.
Dust storms peak during the summer (December
through March), though events in the wintertime(May through August) are also common. Most years
have 15 to 30 moderate to large dust events.

Dust storms are frequent and persistent enoughin this area that they have exposed an open-air
archaeological site along the lake’s edge. The Puesto
Roberts 1 site, located in an old floodplain on thesoutheast side of Lago Colhué Huapi, was first
identified in 2019 when archaeologists noticed thatwinds had exposed a five-centimetre layer of sandy
loam soil littered with stone tools and the bones of awild species of llama called guanaco.
Archaeologists identified 427 artefacts at thesite—including stone cutting blades, milling
tools, scrapers, and egg-shaped bola stones used
for hunting—spread across 15 square metres,
according to a 2022 study led by Heidi Hammond,an archaeologist at the National University of thePatagonia San Juan Bosco. The artefacts, which
are roughly 1,500 to 1,000 years old, are thought
to be the remains of a temporary campsite where
people cleaned and ate guanaco. Most of the stones
were made of chert, a locally available fine-grained
sedimentary rock, but researchers also foundexamples of quartzite, andesite, basalt, xilopal,
rhyolite, black obsidian, tuff, silicified tuff and gneiss
artefacts.
In assessing the size distribution of the artefacts, thesmallest artefacts were notably scarce.
‘Due to the strong erosive action of wind,’ theauthors noted, ‘these types of pieces were probably
mobilised and therefore their representativeness in theassemblage is low.’

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Ship Tracks over the Pacific
MODIS Web Image of the Day

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

Linear clouds crisscrossed the Pacific Ocean off thecoast of California in early April 2024, each marking
the passage of a ship. The Moderate Resolution
Imaging Spectroradiometer (MODIS) acquired thistrue-colour image of the distinctive clouds known as‘ship tracks’ on April 1.
Ship tracks are thin, narrow clouds that form whenwater vapour condenses around the tiny particles
emitted by ships in their exhaust. They don’t form
over every passing ship, but tend to be found wherethin, low-lying stratus and cumulus clouds are alsopresent. Ship tracks often appear brighter thansurrounding clouds, because clouds that form due toship exhaust usually have more and smaller droplets
than do normal, unpolluted clouds. The smaller
droplets scatter light in many directions, and it is
this increased reflectance that makes them appear
white in satellite images.
This area of the North Pacific Ocean is a remarkably
busy waterway, with heavy shipping traffic yearround.
The combination of a high number of ships releasing
emissions and atmospheric conditions conducive tothe formation of a variety of low-level clouds makethe North Pacific a hot spot for viewing ship tracks.

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Landslide Dams the Chilcotin River
NASA Earth Observatory
Story by Adam Voiland

Late on July 30, 2024, landalong the south bank of the
Chilcotin River in Farwell Canyon
began to sink and flow into thevalley below. When the landslide
stopped moving, a large piece ofearth had dropped more than 50
metres, leaving a mound of debris
1,000 metres long, 600 metreswide, and 30 metres deep thatblocked the river and completely
halted its flow.
When the OLI-2 (Operational Land
Imager-2) on Landsat 9 captured
the image shown in figure 1 on
August 1, 2024, water had begun
to pool behind the landslide
deposit, creating a long, narrowlake. Figure 2 shows the same
area on July 16, about two weeks
before the landslide.

Figure 1 - The scene on August 1, 2024 following the landslide

Soon after the event was
discovered, local authorities
issued flood warnings for areas
upstream of the landslide andevacuation orders for areas
immediately downstream.
‘The major threat in situations likethis is that large amounts of waterbuild up behind the landslide damand eventually trigger destructive
outburst floods,’ said Robert
Emberson, a member of NASA’s
Landslides research team andone of the associate program
managers for NASA’s Disasters
program.
On August 5, water began tooverwhelm the natural dam,causing water levels downstream
to increase rapidly and carrywoody debris down the river.
Preliminary modelling from British
Columbia’s River Forecast Center
indicated that water levels would
surge above typical spring flooding
levels on the Chilcotin upstreamof the point where it flows into the
Fraser River.
On the Fraser, estimated flows
are likely to be similar to or below
peak flows that occur during

Figure 2 - The image, acquired on July 16, 2024, shows the scene prior to the landslideNASA Earth Observatory images by Wanmei Liang,
using Landsat data from the U.S. Geological Survey

typical spring flooding. However,‘the water will react differently,
with greater momentum andforce, than a gradual increasein water levels,’ officials from
the Ministry of Emergency
Management and Climate
Readiness (EMCR) warned.
As a trickle and then a gushingtorrent of water chiselled

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through the landslide debris,
authorities urged people to stayaway from the riverbanks dueto the risk of fast-moving waterand debris. A gauge downstream
at Big Bar showed Fraser
River water levels peaking on
August 6 at 3,640 cubic metres
per second: a sharp increase,though not a historical record
for that date.

33

Figure 3 - This photograph shows debris-filled water pooling behind the landslide dam on August 1.
Photo provided by EMCR

‘Fortunately, the Chilcotin River is sparsely
populated, and evacuation warnings have alreadybeen issued,’ Emberson said. ‘But the impact
of flooding on agriculture downstream is still aconcern.’
Figure 3 shows debris-filled water pooling behindthe landslide dam on August 1. Figure 4 shows theleading edge of the floodwater after it broke throughthe dam and flowed south along the Chilcotin River
into the Fraser River on August 5.
The event occurred in a remote part of British
Columbia, about 100 kilometres southwest of
Williams Lake, in an area known as Nagwentled by
the Tšilhqot’in, an Athabaskan-speaking indigenous
group in the area. Nagwentled roughly translates
to ‘landslides across the river.’ Indeed, scars along
the south side of the river, and tongue-shaped
debris fields visible in multiple areas, indicate thatlandslides have occurred relatively frequently.
‘The scalloped edges in the terrain immediately southof the point of failure appear to be ancient landslide
scarps, some of which were likely considerablylarger than the event in July,’ said Daniel Shugar, ageomorphologist at the University of Calgary.

Figure 4 - The leading edge of the floodwater after it brokethrough the dam on August 5.
Photo provided by EMCR

The river is also an important waterway for several
types of salmon. In a statement issued following
the landslide, the Tšilhqot‘in National Government
expressed particular concern that the event had
blocked the movement of Taseko sockeye, an
endangered population that had been on track toreturn to spawning grounds at record low levels prior
to the landslide.

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34

‘[We are] calling on all levels of government,
downstream First Nations, the Pacific Salmon
Commission, and other Nations and States,
especially Alaskan fisheries, to take all
precautionary measures possible to conserve
Tšilhqot‘in territory-bound salmon,’ the group
said.
There are some ranches, farms, and mining
operations along the river edges, and people
regularly canoe and camp along the Chilcotin.
A stretch of the canyon downstream with large
sand dunes is a common destination for hikers,
campers, and mountain bikers. According to the

Canadian Broadcast Company, one person in thearea was partially buried by the initial landslideand had to be rescued by a local resident.
Government officials and university scientists will
be monitoring the situation in the coming days
and weeks from the ground and from the air withhelicopters and uncrewed vehicles using a variety
of technologies. They will also be using satellites
and other forms of remote sensing. “Satellites areindispensable for near-real-time monitoring ofevolving disaster situations like this,” Shugar said.
“Having eyes in the sky to see the entire slide andimpounded lake is tremendously useful.”

Meteor Multi-image Composite
Joachim Scharrer sent in this Meteor M image composite he obtained from four passes of the satellite on July 3, 2024

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This Meteor M2-4 RGB123 HRPT image was acquired by Enrico Gobbetti on August 21, 2024 using the Satdump software.

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36

Home Reef Volcano Grows
NASA Earth Observatory
Story by Lindsey Doermann

NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey

Dry land is ephemeral at Home Reef, a mid-ocean volcano
in the central Tonga islands. Cycles of eruptions anderosion have periodically created and destroyed a small
island there since at least the mid-19th century. In June
2024, an eruption tacked on new area to the speck of land,
lofted a volcanic plume into the sky, and discoloured thesurrounding seawater.
Volcanic activity at Home Reef is on display in this image,acquired by the OLI-2 (Operational Land Imager-2) on
Landsat 9 on June 15, 2024. On that day, lava flowedfrom a vent on the island, according to Tonga Geological
Services, expanding the land that emerged in a September
2022 eruption and causing the coastline to bulge out to theeast.
As a cloud of volcanic emissions streamed west, a plumeof discoloured water flowed east and south, its lighter
colour contrasting with the blue seawater. Previous
research has shown such plumes of superheated acidic
water can contain particulate matter, volcanic rockfragments, and sulphur, as well as precipitates of silicon,
iron, and aluminum oxides.
At other submarine volcanoes, scientists have detecteda change in water colour via satellite imagery up to one

month prior to an eruption, suggesting that ocean colour
could presage a potentially destructive event.
Home Reef sits within the Tonga-Kermadec subduction
zone, an area where three tectonic plates are colliding at
the fastest converging boundary in the world. Here, thePacific Plate is sinking beneath two other small plates,
yielding one of Earth’s deepest trenches and most active
volcanic arcs.
The first recorded eruption at Home Reef dates to 1852,
with another potential island-forming eruption occurringin 1857, according to the Smithsonian Institution Global
Volcanism Program. The volcano reawakened in 1984 and2006, both times creating small new islands and sending
pumice ‘rafts’—concentrated patches of porous, lightweightvolcanic rock—drifting across the ocean surface.
No floating patch of stone was apparent around Home
Reef in June 2024. Nonetheless, ships were advised tostay at least four kilometres away from the island. The
volcanic activity posed low risk to communities on the
nearby Vava’u and Ha’apai island groups, according to
Tonga Geological Services. The agency was also reporting
satellite-detected thermal anomalies at the volcano throughat least June 27.

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37

Tristan da Cunha
NASA Earth Observatory
Story by Adam Voiland

Tristan da Cunha, often said to be
the most remote inhabited islandin the world, is the sort of place
where seabirds outnumber people.
It is part of an island group in theSouth Atlantic Ocean situatedapproximately halfway between thesouthern tips of South America andAfrica. Neighbouring volcanic peaks
within the group include the smaller,
uninhabited Inaccessible Island andthe Nightingale Islands.
The OLI-2 (Operational Land
Imager-2) on Landsat 9 captured
this image of the island group on
May 24, 2023. Tristan da Cunha’shighest point, Queen Mary’s Peak,reaches 2,060 metres above sea leveland displays steep gullies that radiate
downward on all sides.
The island’s vegetation is divided into
distinct zones related to elevation.
Large tussock-forming grasses once
covered the island’s coastal fringes,
but most of this has become pasture,according to the Royal Botanic
Gardens, Kew. Woodlands of Phylica
arborea, known as island cape myrtle,
cover the volcano’s lower slopes (darkgreen) and transition into ecosystems
that include tree ferns, sphagnum
moss, small grasses, bryophytes, andlichens on its upper reaches (lightgreen).

Tristan da Cunha
NASA Earth Observatory images by Lauren Dauphin
using Landsat data from the U.S. Geological Survey

Offshore, underwater forests of giant
kelp surround the islands. The kelp,
Macrocystis pyrifera, is one of thefastest-growing seaweeds on theplanet. Though suspended sediment
may be discolouring the water insome areas, signs of kelp forests(green) are visible in several areas
immediately offshore. In preparation
for an ecological survey of the island’s
marine ecosystems, a team of
National Geographic researchers useddozens of Landsat 7 and 8 images
to locate the likely locations of kelp
forests and plan underwater surveys.
About 240 people live in Edinburghof the Seven Seas, the small town on
the northern edge of the island. The

The Tristan da Cunha group of islands

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38

main occupations are fishing and farming. Many residents
harvest crayfish—sold as Tristan rock lobster—and raise
potatoes and livestock. Away from town, thousandsof birds, including populations of northern rockhopper
penguins, Atlantic yellow-nosed albatross, and broad-billedprion, nest on the small, circular island.
The number of birds might be higher if mice and rats had
not found their way to the islands. Most likely introducedby sailors in the 1800s, rodent populations have boomed
despite an annual rat hunting competition and holiday. The
small mammals are thought to eat large numbers of bird
eggs and young birds.
Ecologists have warned that an abundance of oversized
mice may even be on the verge of pushing a criticallyendangered seabird, the Tristan albatross, to the brinkof extinction on Gough Island (out of the scene to thesoutheast). Another notable species on Inaccessible Islandis the Inaccessible Island rail, the smallest living flightlessbird in the world.
All of the islands are the product of a volcanic hot spot,a type of volcanism that brings magma from deep within
Earth’s mantle. Tristan da Cunha, the youngest andlargest of the group, formed about 200,000 years ago. It
last erupted in October 1961, forcing people on the island
to evacuate. Radiometric dating techniques indicate thatNightingale is the oldest of the three main islands, withvolcanic rocks ranging from 360,000 to 18 million years
old. Inaccessible Island has rocks that range from 1 million
to 6 million years old.

Niagara Falls between Canada and the USA
Copernicus Image of the Day

Credit: European Union, Copernicus Sentinel-2

Niagara Falls are a system of waterfalls on the
Niagara River between Lake Erie and Lake Ontario.
From west to east, the individual waterfalls are
named Horseshoe Falls, Bridal Veil Falls andAmerican Falls. The river flows from southeast
to northwest on this image scene. The water flow
over Horseshoe falls reaches maximum volume
on late spring or early summer days, so this True
Colour Sentinel-2 image of May 30, 2024 probably

captures such a situation. At night, a substantial
part of the water is directed via a system oftunnels to reservoirs and the hydroelectric power
stations located east and west of the river on thenorthern part of the image. Downstream of thefalls, the Rainbow Bridge, the Whirlpool Rapids
Bridge, the Niagara Gorge Rapids and the Niagara
Whirlpool are visible. Two artificial reservoirs arelocated east and west of the river.

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39

Snow Gathers on the Southern Alps
MODIS Web Image of the Day

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

A high-pressure system over New Zealand kept the clouds
away and the sun shining on the gorgeous winter coloursof South Island in mid-July 2024. The Moderate Resolution
Imaging Spectroradiometer (MODIS) on NASA’s Terrasatellite acquired a true-colour image of the bright morning
on July 16.
Snow topped the Southern Alps, which are the rugged
mountain chain that extends for about 650 kilometresalong the western side of South Island. The snowpack is
still thin, relative to deep winter averages, after a mild andmostly dry June. The first week of July brought fresh snow
along with dropping temperatures, which made conditions
perfect for ski resorts to top off the fresh fall with artificial
snow.

According to Mountain Watch, “A significant low from theSouthern Ocean got the season’s ski-tips pointing straight
down the mountain at the start of July though, with some
30-50 cm of fresh snow racking up for most of the resorts”.
Along with snowy peaks, several large valleys of theSouthern Alps are filled with low cloud (fog). Fog appears
tinted slightly tan in this image and has a ground-glass
appearance compared with the sharp, crisp white of thehighly reflective snow. It’s also interesting to compare theappearance of the fog with the clouds over the ocean. The
minor colour differences are primarily due to reflectivity,with the sunlight reflecting off of the smooth surface ofthe snow making it appear much brighter than any of theuneven surfaces of the clouds.

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40

A crystal clear view of Øresund Bridge
Copernicus Image of the Day

Credit: European Union, Copernicus Sentinel-2

The Øresund bridge is one of the longest bridges in
the world, spanning the Øresund straight between
Denmark and Sweden. The bridge connects to atunnel which the road and railway enter on a small
artificial island. The main span is supported bya system of cables on two large pylons: these are
difficult to spot due to their small footprint, but are
nicely highlighted by shadows on this Sentinel-2
image with the sun angle so low. The white spots on
the sea are foam caps of large waves.

Forest fire in Madeira
Copernicus Image of the Day
This image, acquired on
August 18, 2024 by one of
the Copernicus Sentinel-3
satellites, shows a plume ofsmoke 130 kilometres longrising from the Portuguese
island of Madeira as a result ofa large forest fire which started
on August 15.
The fire began in the Serra deÁgua area of Ribeira Brava
and quickly spread to Câmara
de Lobos, where it continued
to pose a significant threat
despite containment efforts.
The flames came close topopulation centres, forcing
the evacuation of at least 100
residents as more than 120
firefighters battled the blaze.

Credit: European Union, Copernicus Sentinel-3 imagery

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41

Currently Active Satellites and Freqencies
Polar APT / LRPT Satellites
Satellite

Frequency

StatusFormatImage Quality

NOAA 15

137.6200 MHz

On

APT

Intermittent sync problem

NOAA 18

137.9125 MHz

On

APT

Good

NOAA 19137.1000 MHz

On

APT

Good

Meteor M N2

137.1000 MHz

Off

LRPT

FailedMeteor M N2-3

137.9000 MHz

On

LRPT

Variable [1]Meteor M N2-4

137.9000 MHz

On

LRPT

Good

Satellite

Frequency

Mode

FormatImage Quality

NOAA 151702.5 MHz

Omni

HRPT

sync problem

NOAA 18

1707.0 MHz

RHCP

HRPT

Good

NOAA 19

1698.0 MHz

RHCP

HRPT

Good

Feng Yun 3C

1701.4 MHz

RHCP

AHRPT

Inactive [2]Feng Yun 3D

7820.0 MHz

RHCP

AHRPT

Active {2}Polar HRPT/AHRPT Satellites

Feng Yun 3E

7860.0 Mz

RHCP

AHRPT

Commissioning

Metop B

1701.3 MHz

RHCP

AHRPT

Good

Metop C

1701.3 MHz

RHCP

AHRPT

Good

Meteor M N2-2

1700.0 MHz

RHCP

AHRPT

Active [8]Meteor M N2-3

1700.0 MHz

RHCP

AHRPT

ActiveMeteor M N 2-4

1700.00 MHz

RHCP

AHRPT

ActiveGeostationary Satellites
Satellite

Transmission Mode(s)Position

Status

45.5°EIODC - On

LRIT (digital)

0°W

Off [4]

HRIT (digital)

LRIT (digital)

9.5°E

On [3]

0.4°W

Commissioning

GVAR 1685.7 MHz

LRIT 1691.0 MHz

61.6°E[5]

Meteosat 9

HRIT (digital)

Meteosat 10

HRIT (digital)

Meteosat 11
MTG-l1
GOES-13GOES-14GVAR 1685.7 MHz

LRIT 1691.0 MHz

105°W

Standby

GOES-15 (W)GVAR 1685.7 MHz

LRIT 1691.0 MHz

135°W

Off (in storage)

GOES-16 (E)GRB 1686.6 MHz

HRIT 1694.1 MHz

75.2°W

On [7]

GOES-17

GRB 1686.6 MHz

HRIT 1694.1 MHz

104.7°W

Off

GOES 18

GRB 1686.6 MHz

HRIT 1694.1 MHz

137.0°W

On [7]

Himawari-8

No direct download

On

No direct download

Data is only available
via the HimawariCast
service140.7°E

Himawari-9

140.7°E

On

Feng Yun 2E

SVISSR (digital)

LRIT (digital)

86.5°EOff

Feng Yun 2F

SVISSR (digital)

LRIT (digital)

112.5°E

Standby

Feng Yun 2G

SVISSR (digital)

LRIT (digital)

105.0°E

On

Feng Yun 2H

SVISSR (digital)

LRIT (digital)

79.0°EOn

Feng Yun 4A

HRIT (digital)

LRIT (digital)

99.5°EOn

Feng Yun 4B

HRIT (digital)

LRIT (digital)

105°E

On

Notes
1
2
3
4
5
6
7
8
9

Currently, M2-3 and M2-4 transmit on 137.9 MHz but have on occasions switched to 137.1 MHz.
Transmission is currently on a Symbol Rate of 72,000 baud, though 80,000 baud has been used in trials.
These satellites employ a non-standard AHRPT format and cannot be received with conventional receiving equipment.
Meteosat prime Full Earth Scan (FES) satellite
Meteosat prime Rapid Scanning Service (RSS) satellite.
Repurposed for use by the US Space Force
GOES 15 also transmits EMWIN on 1692.700 MHz GOES 16 also transmits EMWIN on 1694.100 MHz GOES 17 also transmits
EMWIN
GOES Rebroadcast (GRB) provides the primary relay of full resolution, calibrated, near-real-time direct broadcast space relay ofLevel lb data from each instrument and Level 2 data from the Geostationary Lightning Mapper (GLM). GRB replaces the GOES
VARiable (GVAR) service.
Following a collision with a micrometeorite, the power system aboard Meteor M2-2 has been compromised. AHRPT is still beingtransmitted when the solar panels are sunlit, but there is insufficient battery power to enable the LRPT stream.
Japanese satellites MTSAT-1R (Himawari-6) and MTSAT-2 (Himawari-7) are no longer active and are probably retired. Current
Japanese operational geostationary satellites are Himawari-8 and Himawari-9.

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42