Group for Earth Observation

No 69 - March 2021

This Copernicus Sentinel-1 radar image, acquired on January 28 this year, pictures the two largest fragments of the disintegrated
A68 iceberg. The berg had at one point threatened South Georgia, but in the event, ocean currents carried it safely out of range.
Image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO

Useful User Groups

GEO MANAGEMENT TEAM
General Information
John Tellick,email: information@geo-web.org.uk
GEO Newsletter Editor
Les Hamilton,

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

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

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.

https://groups.io/g/SatSignal

email: geoeditor@geo-web.org.uk
Technical Consultant (Hardware)David Simmons
email: tech@geo-web.org.uk
Webmaster and Website Matters
Vacancy

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

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

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

e-mail: webmaster@geo-web.org.uk
Management TeamDavid Anderson
Rob Denton
Nigel Evans
Clive Finnis
Carol FinnisPeter GreenDavid SimmonsDavid Taylor
www.geo-web.org.uk

2

Les Hamilton

I

t is with deep sorrow that I have to record that Francis Bell, the founder of Groupfor Earth Observation, passed away in early January. For decades, Francis hadliaised with agencies, in particular NOAA and EUMETSAT, to promote free access toweather satellite imagery for the amateur community. He organised numerous GEO
Symposia and three members’ visits to EUMETSAT headquarters in Darmstadt.
Francis was also a well-known face at rallies, manning the GEO Stand and always
ready to give advice to anyone who required it. You can read much more in John
Tellick’s illustrated tribute to Francis on page 13.

S

ince the previous issue, enthusiasts the world over have been following aunique event through satellite images: the ﬁnal breakup of iceberg A68a during
its close encounter with South Georgia. John Tellick followed the event daily via
EUMETcast’s Metop imagery, and has documented his experience, using pictures
to describe what took place far better than any words could. And as one iceberg
ends its journey, another begins after the Brunt Ice Shelf calved A74, a 1270 square
kilometre tabular ‘berg. We’ll follow this up and report in the June issue.

WW

ith the restrictions of lockdown, time has permitted more pages to been
compiled than usual. We hope you enjoy reading them.

e also have expectations of three articles offered by readers, which haven’t
made our publication deadline. Hopefully these will be offered in the June
Newsletter. Any reader wishing to make a contribution should ensure that it reaches
the editor by May 30 at the latest, preferably by email to:geoeditor@geo-web.org.uk

Contents
Quarterly Question
Solar Observatory SOHOA Swirl of Old Supercontinent Silt
Iceberg A68a’s Last DanceIn Memorium: Francis BellThe Grand Bahama Bank
An Inland Delta Flooded
Ice on the Caspian Sea
Introducing NASA Worldwide Snapshots
The Strait of Hormuz
Lake Turkana
The Ocean Odyssey of Iceberg A68a
Cloud-free Iceland
Water in the Etosha Pan
Satellite Status

Fritz Zajicek
NASA Earth Observatory
John Tellick
John Tellick
MODIS Image of the Day
NASA Earth Observatory
MODIS Image of the Day
Les Hamilton
MODIS Image of the Day
MODIS Image of the Day
Les Hamilton
European Space Agency
MODIS Image of the Day

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29
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34
35
36

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Quarterly Question 67
The question posed last December concerned a bodyof water surrounded by snow-capped mountain
ranges. The lake in question is Issyk-Kul (pictured
opposite), which lies amidst the Northern Tian Shan
mountains in Eastern Kyrgyzstan.
A saline endorheic lake with no riverine outlets,
Issyk-Kul is notable as being the seventh deepest
lake in the world, with an average depth of 278
metres and plunging to a maximum depth of 668
metres. Not surprisingly, Issyk-Kul contains a vastquantity of water, over 1700 cubic kilometres ofit, making it the tenth largest lake in the world by
volume.
The name Issyk-Kul means ‘warm lake’ in the
Kyrgyz language because, despite being surroundedby snow-capped peaks, it apparently never freezes
over, probably because the lake is fed by a numberof hot springs. The lake is a Ramsar site of globallysignificant biodiversity and forms part of the IssykKul Biosphere Reserve.
Future Quarterly Questions?
The Quarterly Question was devised by Francis
Bell as a—generally straightforward—puzzle for

GEO Quarterly readers, and frequently based on
his experiences when visiting over 100 countries
worldwide. If any reader feels inclined to continue
the tradition, please feel free to send materials to theeditor atgeoeditor@geo-web.org.uk

at least one week prior to the month of publication.

Two weeks after a spell of sub-zero temperatures, and one week following a thaw and devastating flooding, summer
arrived early in the British Isles, as seen in this LRPT image from Meteor M2 on the last day of February.

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Solar Observatory SOHO: 25 Years in Space
Fritz Zajicek OE3FZBGEO Newsletter readers, mostly amateur enthusiasts
and educational users, usually focus on receiving andobserving weather from Earth imaging satellites. But what
would our mother Earth be without the sun. So, let’s take alook to our central celestial body and the SOHO spacecraftthat has been observing it for a quarter century now.
The Solar and Heliospheric Observatory (SOHO) was
built as a joint project between the European Space
Agency (ESA) and the US National Aeronautics andSpace Administration (NASA), by a European industrial
consortium led by Matra Marconi Space. Other sources
mention the lead management by Astrium, an EADS
Company, later Airbus Defence and Space, now
Airbus SE). It was first proposed 13 years before its actual
launch.
SOHO was launched 25 years ago on a Lockheed Martin
Atlas II-AS launch vehicle on December 2, 1995 andbegan normal operations in May 1996. It occupies a halo
orbit around L1 (Lagrangian Point 1), 1.5 million kilometres

SOHO - folded for Transport
Credit: SOHO (ESA & NASA) / Wikimedia Commons

Mission Details
Originally planned to study the Sun as a two-year mission(with a constructive nominal lifetime of 3 years), SOHO
continues to operate after over 25 years in space. The
mission has now been extended till December 2020, withindicative extensions for an additional two years, up to
2022. This decision was taken during the ESA’s Science
Programme Committee (SPC) meeting in November 2018.
PayloadThe SOHO Payload Module (PLM) consists of twelve
instruments, each capable of independent or coordinatedobservation of the Sun or parts of the Sun. Nine
instruments came from multinational teams led by
European scientists, and three from US-led teams. Some
instruments are no longer fully functional or have been
deliberately retired due to symptoms of old age.
Artist’s concept of the NASA SOHO spacecraft
Image credit: Cgruda, Public domain, via Wikimedia Commonscloser to the Sun than the Earth, from where it enjoys
uninterrupted views of our star.
The spacecraft dimensions are 4.3 x 2.7 x 3.65 metres,with a launch mass of 1850 kg and a scientific payload
mass of 610 kg. The electrical power of 1500 W isprovided by a solar array with 9.5 metre span and 950 W
from two 20 Ah Ni Cd batteries.

Objectives
The mission was launched with three scientific objectives
in mind. The first was to study the dynamics and structureof the solar interior. The second was to study why theSun’s outer atmosphere, the corona, is so much hotter
than its surface, and the third was to study where andhow the solar wind particles are accelerated. But perhaps
the most important aspect of SOHO’s work has beensomething that was only just coming to prominence at thetime of its launch: the study of space weather.

www.geo-web.org.uk

5This graphic highlights some of the SOHO mission’s impressive numbers to date
Image credit: ESA, via eoPortal.

The image at left is an artist’s
impression of the ESA/NASASOHO spacecraft, backed by
an image of the Sun acquiredby the satellite’s extremeultraviolet imaging telescope on
September 14, 1999.

Image credit: Spacecraft: ESA/ATG
medialab; Sun: ESA/NASA SOHO, CC
BY-SA 3.0 IGO, via eoPortal

In the last 25 years SOHO could thus observe more than
two of the eleven-year solar cycles, collected around
50 TB of data and sent 20 million images to the scientists
on Earth.
In addition to investigating how the Sun works, SOHO
is the most prolific discoverer of comets in astronomical
history, having spotted more than 4000 of these icy bodies
during the sunward leg of their journeys.
Almost 6000 papers have now appeared in refereed
journals based on SOHO data as an outcome of thespacecraft mission. Many of these represent significant
progress in our understanding of the original objectives,
the better understanding of solar processes and theirinfluence on our Earth.

SOHO remains the flagship of solar research probes.
References:• Max Planck Institute for Solar System Research(MPS) https://www.mps.mpg.de/en• MPS News - Solar Observatory SOHO: 25 years inspace https://www.mps.mpg.de/solar-observatorysoho-25-years-in-space• ESA Earth Observation Portal (eoPortal) https://directory.eoportal.org/web/eoportal/home• eoPortal - SOHO (Solar and Heliospheric
Observatory) https://directory.eoportal.org/web/
eoportal/satellite-missions/s/soho• Wikipedia (in different languages with slightly different
content) - https://en.wikipedia.org/wiki/Solar_and_
Heliospheric_Observatory

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NOAA 20 captured this image of Storm Bella at 13.30 UT on December 20, 2020 as the enormous depression
engulfed the UK, France, Belgium and The Netherlands. Responsible for serious flooding across southern
England, the storm produced winds of 160 kph over the Needles near Penzance, and caused disruption at
Schiphol Airport as pilots struggled to land aircraft in 90 kph winds.
Image: NASA Worldview Snapshots (https://wvs.earthdata.nasa.gov/)

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A Swirl of Old Supercontinent Silt
NASA Earth Observatory
Story by Adam Voiland.

The Svalbard archipelago between
mainland Norway and the North Pole,is known as a mecca for geologists. It
is one of the few places in the worldthat has easily accessible rocks fromnearly every geological time period.
There is little soil or vegetation tocover up the remarkable geologic
diversity. Despite the Arctic location,
ocean currents moderate the weather
enough to keep much of the land
clear of snow in the summer.
Among the more striking geologic
attractions, at least when viewed
from above, are glaciers on thearchipelago’s northwestern island of
Spitsbergen. The ice there seems
to ‘bleed’ meltwater of an intense
shade of red. The Operational Land
Imager (OLI) on Landsat 8 acquired
figure 1 showing red water poolingin a shallow meltwater lake near
the terminus of Holmström glacier.
The image was captured on August23, 2020, shortly after an unusual
heatwave brought record-breaking
temperatures to Svalbard. Figure 2
shows a wider view. Note that theimage has been rotated to combat
relief inversion, an optical illusion thatcan make valleys look like mountains.
The red colour is due to anabundance of sediment that has
sloughed off from a particularly ironrich layer of rock that formed roughly
400 million years ago (during the
Devonian Period). Sometimes called
the Old Red Sandstone, the rocklayer formed on land when sandand other sediments were trappedin a basin enclosed by series ofmountain ranges. The mountain
ranges emerged when several of theworld’s land masses were smashedtogether in a supercontinent called
Laurussia, sometimes called the Old
Red Continent.
“The red Devonian rock is fairly
soft and erodes easily,” explained
University of Edinburgh geologist
Geoffrey Boulton. “Glacial
grinding produces a great dealof silt. These very small—and in

Figure 1 - Landsat-8 captured this image on August 23, 2020.

this case red—particles are easilysuspended in flowing meltwaterand take a long time to settle instill water.”of the moraine. The stream eventuallywidens and meanders some as
it moves through mud flats as it
approaches the sea.

The silty meltwater pooled first in ashallow lake that had formed behind
Holmström’s push moraine—a damlike pile of sediment bulldozed by thefront of the glacier when it surged
about a century ago. Since then, adrainage stream has carved a narrow
channel through the folded sediments“When the silty water reaches
seawater in Ekmanfjorden, it
stays at the surface because thefreshwater has a lower density
than saltwater,” explained Boulton.
NASA Earth Observatory images by
Joshua Stevens, using Landsat data fromthe U.S. Geological Survey.

Figure 2 - A wider Landsat view over the area.

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Iceberg A-68a’s Last DanceJohn Tellick
Les Hamilton has written an article describing the giant
iceberg’s travel from the Southern Ocean and its drift
towards South Georgia (page 31).
Thanks to Metop’s world AVHRR imaging coverage via
EUMETCast meteorological data dissemination, we
have been able to witness—cloud cover permitting—the
gyrations of its final journey, fragmentation and break-up.
The iceberg started life as a very large ‘chunk of ice’ whichbroke away from the Larsen Ice Shelf of Antarctica (seeaerial photos on page 12). By the time it arrived in theneighbourhood of South Georgia it had lost much of its
mass, yet was still larger than the island of South Georgia
and had an estimated draft of 200 metres. It was predictedthat it would ‘beach’ on the island shore and cause anenvironmental catastrophe to local wild life.

Figure 3 - December 14: the iceberg, still intact, starts to turnaway from South Georgia.

However as Les Hamilton explains, thankfully, due to theeffects of local undersea terrain and ocean currents, it
drifted (was nudged?) past and avoided the island. From
December 2020 to February 2021 it gyrated on its journeyas the following sequence of Metop images shows.
All images © EUMETSAT 2020/2021

Figure 4 - December 17: The top left hand corner fractures.

Figure 1 - What was left of the original iceberg as it drifted
towards South Georgia on December 9, 2020.

Figure 2 - December 11: Possibly the closest approach of theiceberg to South Georgia.

Figure 5 - December 22: The base of the finger is fracturing
as the iceberg moves further away from the island. The darkhorizontal line across the main area is due to cloud shadow andis not a fracture.

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Figure 6 - December 25: The finger moves off and another lower
right fracture develops.
Figure 10 - January 6: The finger is now drifting further away fromthe main block.

Figure 7 - December 29: The finger moves around the main
surviving fragment of A68a.

Figure 11 - January 7: The finger drifts further north.

Figure 8 - December 31: The main block turns with the finger.

Figure 9 - January 1, 2021: The main block is still turning.

Figure 12 - January 11: The finger turns on a path that goesaround the north of South Georgia.

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Figure 13 - January 17: The finger turning again as the main
block rotates and moves away from South Georgia.

Figure 16 - January 30: The main block, having turned again,
now starts breaking up.

Figure 17 - February 11: After a week of cloud, the fractured
pieces of A68 A appear under the clouds.

Figure 14 - January 23: The finger turns slightly again.

Figure 18 - February 12: Another view of the break-up.

Figure 15 - January 27: The finger turns again as does the main
block of A68a.

Figure 19 - February 16: The fractured pieces disperse.

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On November 12, 2017, NASA’s Operation IceBridge—the airborne mission flown annually over both polar
regions to map the ice—photographed the recently calved A68a tabular iceberg. John Sonntag, IceBridge
mission scientist, shot this photo from a window of the P-3 research plane.
NASA photograph courtesy of NASA/John Sonntag

The edge of A-68, the iceberg the calved from the Larsen C ice shelf.
NASA photograph courtesy of NASA//Nathan Kurtz.

www.geo-web.org.uk

12In Memorium: Francis BellJohn Tellick

Francis Bell, photographed in his ‘shack’ during a GEO Management Meeting in 2004
Photo: David Taylor

GEO members will have been saddened to hear ofthe death of our Director and Chairman, Francis
Bell, who was the inspiration behind the formationof GEO. The GEO management team and the many
GEO members who met Francis over the years at
Rallies and Symposia will miss him greatly.

Around 2002, Francis was at the forefront of a moveto create a more amateur -run and independent
organisation dedicated to Earth Observation, and
the Group for Earth Observation (GEO) was formallycreated in 2003, with the Launch Edition of GEO
Quarterly following in March 2004.

Francis had perhaps a bit of a father figure persona
about him—I guess this was a throwback from hisdays as a master at The Royal Grammar School in
Guildford.

This coincided closely with the failure, early in its
test phase, of a Solid State Power Amplifier (SSPA)
aboard the newly launched MSG-1: the first of theSecond Generation ‘all digital’ Meteosat satellites.
This resulted in the decision that it would not beable to transmit ‘direct dissemination’ from thissatellite to users as had been the system for theFirst Generation Meteosats. This forced EUMETSAT
to adapt a new transmission system that they had
been using for NOAA sounding data, that was toprove particularly beneficial to amateur enthusiasts.
MSG-1 data would be rebroadcast from a commercial
TV satellite, and I’m pleased to say that several
members of both GEO andMy friendship with Francis goes back very many
years: to the days of RIG in fact. Francis was along time member of the committee, and served two
spells as Chairman of the Group. We both enjoyedattending radio rallies and demonstrating live
WEFAX and APT images on the RIG stand.
Francis organised two great and very well attended
AGM/activity days at the Royal Grammar School for
RIG.

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Francis Bell (front row left) poses with the GEO party during the inaugural Darmstadt visit in 2007.
Photo: EUMETSAT

our Dutch friends in Werkgroep Kunstmanen took
part and worked with EUMETSAT in extensive
testing: reporting problems and ‘fixes’ and proving
the robustness of the new DVB-S data service whichbecame EUMETCast. Francis, David Simmons andmyself then spent several happy and fun years
demonstrating live EUMETCast reception at radio
rallies with an 80 cm dish and ‘off the shelf’ domestic
satellite TV receiving equipment.
Francis was very keen to maintain the close
relationship that GEO had built up with EUMETSAT
during these tests and exchanges, and worked
tirelessly to bring to fruition a project close to hisheart. This was an organised two-day visit by a partyof GEO members to EUMETSAT’s Darmstadt HQ in
2007. This was hosted by EUMETSAT, in their large
conference centre, with many technical presentations
given, plus a guided tour of all the EUMETSAT
technical and operational areas. Some of GEO andWerkgroep Kunstmanen’s ‘technical experts’ also had
a very useful meeting with EUMETCast engineers.
On the second day of the trip we enjoyed a guided
tour of the large Usingen ground station nearFrankfurt where the massive Meteosat reception andcontrol dishes were installed, and where the new
EUMETCast service was uplinked to the commercial
satellite. Francis had also organised a conducted
tour of the ESA main Control Centre (ESOC) in
Darmstadt, including the satellite control room.
Evenings during the trip were spent enjoying a greatsocial get-together with some of EUMETSAT’s staff
over dinner. So successful was this venture, that it
was repeated in 2011 and 2015.
Francis also organised eight GEO Symposium’s
between 2002 and 2014, most of them held at the
National Space Centre in Leicester, where he wasably assisted by his wife, Nadine, who looked after
our welcome, registration and refreshments of coffee
and biscuits during the day. In 2012, in place ofa symposium, Francis organised a visit to Surrey

Francis and friends enjoying a convivial dinner at
the conclusion of the 2011 Darmstadt visit.

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Francis (2nd from right) with the GEO party just prior to their visit to Surrey Satellite Technology Ltd in 2012.
Photo: Baz Omidi

Satellite Technology Limited(SSTL) where the GEO party
were taken on a guided tour ofthe premises.
GEO management teammeetings were often hosted by
Francis at his house in Surrey—
where the sun always seemed toshine and where we spent happy
breaks in the garden ‘awayfrom the table’. These meetings
always culminated in the mostwonderful dinner, cooked by
Nadine, always with second
helpings of ‘main’ and pudding.
It was generally very late in theevenings before we finally brokeup, and those who had travelledfrom far afield were admirablyaccommodated overnight by
Nadine and Francis.
These were very happy days andremembrances of Francis, andhe will be hugely missed. The
photographs on the following
pages reflect Francis’ activities
during his time with GEO, andwill undoubtedly stir many fondmemories for many readers.

Almost everywhere he travelled, Francis delighted in taking his minimalist, portable APT kit
with him, sometimes even resorting to the use of a simple antenna fashioned from a metalcoat hanger. Here he is pictured on location with a turnstile antenna.

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Francis congratulating Arne van Belle on his presentation at the2009 GEO Symposium held in the Royal Grammar School.
Photo: David Taylor

Francis Bell, with wife Nadine (left) and Minh van den Bosch,pictured following the Symposium in the Royal Grammar School.
Photo: David Taylor

Francis, pictured centre, with members of the GEO party at Usingen next to the T-Systems
EUMETCast DVB-S uplink dish (at right) during the 2011 Darmstadt visit.
Photo - Arne van Bellewww.geo-web.org.uk

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The day/night sensor aboard NASA’s Suomi-NPP satellite captured this image showing
auroras over Alaska and western Canada on February 7, 2021.
Image: NASA

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The Grand Bahama Bank
Modis-Web Image of the Day
https://modis.gsfc.nasa.gov/gallery/showall.php

Peacock blue and gem-like greens colour the waters
off the Bahamas. While the variation of colours andsweeping curves are reminiscent of gentle brushstrokes laid down by a master painter, they are theresult of a combination of shallow depth, unevencontours of the ocean floor, sea grass banks, and thelight-coloured sands that form the Great Bahama
Bank.
The Great Bahama Bank is a massive underwater
hill underlying Andros Island in the west, Eleuthera
Island in the east and multiple islands in between. It
reaches almost to northeastern Cuba, which can beseen near the bottom of the image.
In past ice ages, the Great Bahama Bank was dry
land, but as ice melted and sea levels rose, thetall hill slowly submerged under the ocean. Today,the bank is covered by water, though it can be

as shallow as two metres deep in places, while
the surrounding basin drops to depths as low
as 4,000 metres. The bank itself is composed ofwhite carbonate sand and limestone, mainly fromthe skeletal fragments of corals. Where the depth
plunges, the ocean appears deep blue.
Between Andros Island and Eleuthera Island, a long
deep, dark region that is known as the Tongue of the
Ocean, where the depth drops to 2,000 metres. An
important area rich in sea life, it is home to morethan 160 fish and coral species. At the southernedge of the Tongue of the Ocean, colourful waveshaped ripples can easily be seen from space. These
are underwater dunes on the Great Bahama Bank,
sculpted by currents over time. Sand and sea grassfound in the dunes add to the striking colours of thisarea. The dunes are partially covered by cloud in thisimage.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra satelliteacquired a true-colour image of the Great Bahama Bank on November 30, 2020.
Image: NASA

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An Inland Delta Flooded
NASA Earth Observatory
Story by Adam Voiland

Drought is a perennial problem in the semi-arid
Sahel region of Africa. But in 2020, in Mali andother countries in West Africa, excessive rainfall
has been the problem at times. Exceptionallyheavy summer rains pushed seasonal floods
on the Niger River and the Macina (theInland Niger Delta) to destructive levels.
After intense rains fell in July and August in
the Guinea Highlands and overloaded many
streams and rivers, it took several weeks forflood waters to work their way through the vastinland delta in central Mali. When the Moderate
Resolution Imaging Spectroradiometer (MODIS)on NASA’s Terra satellite captured a naturalcolour image on October 29, 2020, water had
spread widely across the nearly flat delta, which
was once a lake bottom. Standing water appears
black. Many flooded areas appear green because
bourgou grass, rice, and other plants grow in theshallow flood waters. For comparison, the otherimage shows the dry landscape in May 2020,
before the rains.
In late October, floodwaters reached their peakheight at Mopti, a town at the confluence of the
Niger and Bani Rivers. Water levels in the delta
were recorded at 670 centimetres on October
26 and remained at that level until November 2,
according to Mali’s National Directorate of Water
Resources. That tied the peak water levels from2018, the highest since 1969.

The dried out Macina, imaged during May 2000.
NASA Earth Observatory images by Lauren Dauphin, using MODIS
data from NASA EOSDIS/LANCE and GIBS/Worldview.

After November 2, waters receded at Mopti evenas they continued to rise at points downstreamsuch as Akka and Diré. It typically takes watera full six months between falling in the Guinea
Highlands and reaching the ocean at the Niger
Delta in Nigeria. People watch the timing offlooding closely because it affects when rice canbe grown, when fish will be available to catch,
and when pastures can be ready for grazing.
Water levels were expected to be low enoughin mid-December 2020 for the annual cattle
crossing on the Niger River at Diafarabé. In themuch anticipated event, nomadic herders drive
cattle across the river toward rich grazing landsin the inland delta and are reunited with theirfamilies after months apart.
While seasonal floods are common in Mali,
the severity of the floods this year caused
widespread damage. The United Nations Officefor the Coordination of Humanitarian Affairs
estimates that 1,160 homes were destroyed byflooding.

The Macina following Niger floods, imaged on October 29, 2000.
NASA Earth Observatory images by Lauren Dauphin, using MODIS
data from NASA EOSDIS/LANCE and GIBS/Worldview.

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Storm Darcy brought The Netherlands its first major snowstorm for a decade, encasing the country in snow and ice and prompting
thousands of skaters to take to the ice. NOAA 20 imaged the deep-freeze on February 11, 2021.
Image: NASA Worldview Snapshots (https://wvs.earthdata.nasa.gov/)

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Readers’ Images

André T’Kindt created this composite image from passes of NOAAs 15, 18 and 19 on December 13, 2020.
Created in WXtoImg, using the MCIR precipitation option.

Joachim Scharrer sent in this Meteor M2 image showing a plume above mount Etna on December 15, 2020.

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Ice on the Caspian Sea
Modis-Web Image of the Day
https://modis.gsfc.nasa.gov/gallery/showall.php

Sitting at the crossroads between
Europe and Asia, the Caspian Sea
claims the title of Earth’s largest
land-locked inland water body.
It covers roughly 371,00 square
kilometres) and borders fivecountries. Russia sits along thenorthwestern shore, and moving
clockwise come Kazakhstan,
Turkmenistan, Iran, andAzerbaijan.
Although it is often called a lake
and receives fresh water fromroughly 130 rivers, including themighty Volga, the waters of the
Caspian Sea are saline. While theoverall saltiness is about one third
as much as the ocean, the salinity
is not uniform. In the north,where the rivers enter, the wateris freshest, and the southernwaters are saltiest. The depth ofthe lake changes dramaticallybetween north and south as well.
Most of the north area sits overa shelf, leaving a depth of only
10 metres or less, but the depth
drops to hundreds of metres inthe south, reaching as much as
1,000 metres in some places.

column than deeper water, andthe rapid cooling of the watercolumn facilitates freezing. These
factors explain why the northern
Caspian Sea reliably freezes in thewintertime, while the southern
section usually remains ice-free.

As winter comes to the CaspianSea, frigid temperatures embrace
the northern regions first, bringing
frost to the land and encouraging
ice formation. But more than
air temperature affects freezeup of the Caspian Sea. Salinityand depth also are importantfactors. Fresh water freezes at
0°C, but when salt is present thefreezing point drops. For every fiveparts per thousand salt content(salinity), the freezing point
drops by 0.28 °C. Additionally,shallower water cools more
readily throughout the water

The Moderate Resolution Imaging
Spectroradiometer (MODIS) on
board NASA’s Aqua satelliteacquired this true-colour image of
the Caspian Sea on December 3,
2020. Bright, white fast‑ice clings
to the shore of Kazakhstan while
open water can be seen near theVolga River Delta and southward.
Tan sediment pours into the
Caspian Sea from the Volga Riverand changes colour to green as it
sinks into the blue waters of the
Sea.

Image Credit: MODIS Land Rapid Response Team, NASA / GSFC.

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Late January 2021 brought heavy snowfalls to much of Great Britain, particularly western areas. NOAA 20 captured thisalmost cloud-free image of the island on January 25, with urban areas standing out as grey spots in the blanket of white.
Image: NASA Worldview Snapshots (https://wvs.earthdata.nasa.gov/)

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Introducing NASA Worldview Snapshots
Les Hamilton
For many years, high resolution
Level-1 image segments fromNASA’s Terra and Aqua satellites
were regularly available fordownload, in near real-time, via
the LANCE-MODIS website: manyof the images that have appearedon the pages of GEO Quarterly
over the years had been sourced
from here. But this web page is
now gone, replaced by the NASA
Worldview Snapshots web page.
The NASA Worldview Snapshots
interface is pretty straightforward
to use and comes with a numberof new features. It provides
imagery that is already rectified(free from the ‘bow-tie’ effect thatusers previously had to correct
themselves), offers options to add‘Coastlines’, ‘Coastlines, Borders& Roads’ and ‘Fires’, and includes
imagery from both the Suomi-NPP
and NOAA 20 satellites in addition
to Terra and Aqua.
The scope is wide ranging. In
addition to making near real-time
imagery available approximately
three hours after acquisition,
NASA Worldview Snapshots also
includes a huge library of historicsatellite imagery dating back to
the date each satellite became
fully commissioned. For example,
the Terra satellite was launched on
December 18, 1999 and, by using
the ‘Calendar’ feature, images canbe recovered from as long ago as
February 2000.
Getting Started
You can access Worldview
Snapshots at the following URL

Figure 1 - The main Worldview Snapshots Page

https://wvs.earthdata.nasa.gov/

which displays the pageshown in figure 1. Worldview
Snapshots provides you withaccess to imagery from theModerateResolution Imaging
Spectroradiometer (MODIS)
carried by NASA’s Aqua and Terrasatellites as well as the Visible
Infrared ImagingRadiometer(VIIRS) aboard both the Suomi-NPP
and NOAA 20 satellites.

Figure 2 - Selections from zoomed map: British Isles (left) and South Georgia.

Selecting a Date and Region
Start by using the ‘Calendar’ toselect an appropriate date, thenoutline the region required on
the map. For ease of use, thewww.geo-web.org.uk

map may be zoomed and dragged
around using the controls to its
right. Hovering the mouse overeach control reveals a pop-up
window defining its function. The

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area required is then defined bydrawing a rectangle around itwith the selection tool. Figure 2
provides two illustrations of this.
Satellite Selection
Clicking the drop-down menu
beneath ‘Base Layer’ (figure 1)
displays the options shown infigure 3. For most purposes you
will select the True Color option
which combines frequencies
that provide natural-looking
images of land surface, oceanicand atmospheric features. Other
frequency combinations produce
false colour images designed tohighlight specific features suchas snow, ice and burn scars. If
you are interested, do visit theFrequently Asked Questions (FAQ)
link in the How to Use section of
the main Worldview page to learn
more.

Figure 3 - Bare Layer Options.

Image Resolution
Clicking the ‘Resolution’ option
reveals a drop-down menu
offering image resolutions between
250 metres and 10 kilometres
per pixel. The highest resolution
possible for the area you selectwill be denoted with an asterix asshown in figure 4.

Figure 4 - Resolution options

Generating an Image
With these basics completed,click the orange Preview Button
at the foot of figure 1 (you canalternatively, click the Download
Button if you are confident of the
final rendition). This reveals thePreview Screen (figure 5), where,
if all is well, you again have theoption to download the image.

Figure 5 - The Preview Screen

The advantage of using thePreview Screen is that it allows
you to check the image of thearea from each satellite in turnand select the one that suits yourneeds best: for example, which
one is least obscured by clouds.

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The Worldview image archive
consists of spliced satellite passes
and, if you are unlucky in yourchoices, there may be an obtrusive
line of discontinuity slanting
across an image where cloudfeatures do not match precisely,25

Figure 6
This December 26, 2020 Suomi-NPP image of South Georgia
and the disintegrating A68 tabular ice slab clearly illustrates
the discontinuity where adjacent satellite passes have been
integrated together.

as illustrated in figure 6, which shows the A68a
iceberg and South Georgia. By temporarily closing
the Preview Screen (click the ‘x’ at the top rightcorner) you return to the main screen where you
can select a different satellite and click the preview
button again. You can repeat this for all/any of thefour satellites and would be unfortunate indeed if
none of the preview images was acceptable. Now you
can download your selected image with confidence.

Figure 7
This Worldview Snapshot of the Great Lakes, acquired on July17, 2020, illustrates the Autoscale feature. The upper image wasdownloaded with Autoscale deselected, whereas, for the more
‘normal looking’ lower image, Autoscale was selected.

AutoscaleThe ‘Auto Scale’ feature scales the width of images,
particularly at higher latitudes, to create a betterlooking, more psuedo-equal-area image. ‘Auto Scale’is selected by default. Figure 7 illustrates the use ofthis feature.
Fires
Checking the ‘Fires’ option on the interface places asmall orange dot at the source of wildfires. Figure 8
illustrates this for the spate of wildfires near Los
Angeles on August 2, 2020.
Rolling Back TimeIf you wish to view historic images from long ago,
opening the ‘Calendar’ and scrolling back month bymonth is time consuming. Instead, click on the year
below ‘Layer Date’ to select it, and use the keyboard
down-arrow key to scroll, one year at a time as in
the illustration below.

Figure 8
Wildfire hotspots near Los Angeles on August 2, 2020.

Following a Trend
Useful features at the foot of the Preview Screen
are two buttons labelled ‘Prev’ and ‘Next’. These
allow you to view precisely the same area daily overa period of time, useful for following the progressof an extended event. I followed the breakup of
iceberg A68A throughout December and January
in this manner, saving the clearest images from thesatellites to create the montage in figure 9 overleaf.

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December 3, 2020
Aqua

December 8, 2020
Suomi-NPP

December 11, 2020
NOAA 20

December 13, 2020
Suomi-NPP

December 14, 2020
Suomi-NPP

December 18, 2020
Suomi-NPP

December 20, 2020
Terra

December 25, 2020
Aqua

January 1, 2021
NOAA 20

January 9, 2021
Suomi-NPP

January 17, 2021
Terra

January 26, 2021
Suomi-NPP

Figure 9This sequence of images illustrates the breakup of tabular iceberg A68a between early December 2020 and late January 2021.
www.geo-web.org.uk
Credit: NASA
Worldwide Snapshots (all images)

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The Strait of Hormuz
Modis-Web Image of the Day
https://modis.gsfc.nasa.gov/gallery/showall.php

The narrow Strait of Hormuz lies between the
Persian Gulf and the Gulf of Oman, separating
Iran to the north from the Arabian Peninsula onits south. Only about 34 kilometres wide at thenarrowest point and roughly 155 kilometres long,
about thirty percent of the world’s seaborne oil andnearly one-quarter of the liquefied natural gas (LNG)
supply passes through this strait—all on shipping
lanes only three kilometres wide. It has been
estimated that 21 million barrels of oil, with a valueof 1.2 billion US dollars (USD), pass through thestrait every day.
The arid landscape of Iran sits in the north, with
Qeshm Island, the largest in the Persian Gulf, justoff the Iranian coast. The tiny Strait of Khuran
separates the island and the mainland and bounds

a wetland of international importance, recognised byRamsar [1]. These wetlands provide critical habitat
to two globally threatened species: the Dalmatian
Pelican and the Green Sea Turtle. In the south, therocky and rugged Musandam Peninsula juts into theStrait of Hormuz. The tip of the peninsula is filled by
the Musandam Governate, and exclave of Oman. To
the south, the land on the peninsula belongs to theUnited Arab Emirates.
Reference
1 The Ramsar Convention on Wetlands of International
Importance is an international treaty for theconservation and sustainable use of wetlands. It isalso known as the Convention on Wetlands. It is
named after the city of Ramsar in Iran, where theconvention was signed in 1971.

On December 2, 2020, the Moderate Resolution Imaging Spectroradiometer (MODIS) on
board NASA’s Terra satellite acquired this true-colour image of the Strait of Hormuz.
Image: NASA

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Lake Turkana
Modis-Web Image of the Day
https://modis.gsfc.nasa.gov/gallery/showall.php

Image Credit: MODIS Land Rapid Response Team, NASA GSFC

Lake Turkana has been called ‘The lake that tells
the story of humanity’s birth’. Seated in East Africa’s
Rift Valley, this saline lake stretches for more than
249 kilometres) and measures only 44 km in width,
providing scarce water resources in a very dry
landscape. More than two million years ago, however,the lake was larger and the surrounding countryside
more hospitable. Palaeontologists have discovered
fossils dated as early as 3.4 – 4.2 million years in
the Turkana basin on the west side of today’s lakeboundaries, which include ancient fish, turtles,
rodents, horses, elephant and primates, evidence of
the abundant life found in this region in times past.
In the 1960s, scientists began to work the fossil
beds on the east side of the lake. Tools that showed
the handiwork of humanity were found in sediment
dated at 3.3 million years old. In 1972, a team leadby Richard Leakey discovered a skull and somebones that were subsequently dated back 1.9 million
years. This early hominid, Homo rudolfensis, was justone of three hominid species that coexisted in thisregion between 1.78 and 1.98 million years ago. In
1984, the nearly complete skeleton of a boy who lived
between 1.5 and 1.6 million years ago was foundnear Lake Turkana. Known as Turkana Boy, he is
one of the earliest examples of Homo erectus known.
The ancient sediments and sandstone of Lake
Turkana have truly revealed much about our planet’s
ancient history, and the dawning of our species.
______On December 10, 2020, the Moderate Resolution
Imaging Spectroradiometer (MODIS) on board NASA’s
Aqua satellite acquired this true-colour image ofLake Turkana. Sediment stains the waters, especiallyin the muddy-coloured northern end. Lake Chew
Bahir, the small lake northeast of Lake Turkana, isalso stained with sediment. Lake Chew Bahir and thenorthern tip of Lake Turkana lie in Ethiopia while
the southern section of Lake Turkana belongs to
Kenya.

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In the aftermath of Storm Darcy, the Suomi-NPP satellite captured this image of snow-covered Scotland on February 11, 20231.
With the winds coming from the east, the west coast and islands largely escaped the snow. Indeed, just two date later, conditions on
Skye were so tinder-dry that wildfires broke out.
Image: NASA Worldview Snapshots (https://wvs.earthdata.nasa.gov/)

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The Ocean Odyssey of Iceberg A68a
Les Hamilton
Regular readers may recall one of our articles in 2017
which detailed the calving of the A68 tabular iceberg
from the Larsen‑C ice shelf in Antarctica on July 12 thatyear [1]. Considerable interest was expressed at the timeowing to its size: measuring 175 × 75 kilometres, with asurface area of 5800 square kilometres, it was the fourthlargest tabular iceberg recorded during the satellite era.
As a guide, its area was approximately twice the area of
Luxembourg.
A68a became virtually becalmed for several months, andby November that year had drifted a mere five kilometresfrom the Larsen‑C ice shelf. Although A68 was largely toremain intact during the following three years, it did lose a
65 square kilometre chunk shortly after calving, which was
designated iceberg A68b, the parent ‘berg being renamed
A68a.
But interest waned over the following two years as A68a
made extremely slow progress north across the Weddel
Sea. It was not until February 2020 that the iceberg finally
cleared the Antarctic Peninsula and moved into the open
waters of the Southern Ocean, where winds and currents
hastened its drift northwest in the general direction ofSouth Georgia.
By early November 2020 it had become clear that it was
highly possible that A68a, which figure 1 shows to beconsiderably larger than South Georgia, might actually
ground on the shallower continental shelf near the island,
posing a serious threat to its colonies of seals andpenguins. The iceberg’s close position to the remote island
prompted fears that it might anchor itself to the coast andimpact the fragile ecosystem that thrives around the island,through the scraping of the seabed or the release of cold
freshwater into the surrounding ocean. The map in figure 2
shows the continental shelf around South Georgia.

Figure 1
A68a and South Georgia Imaged by NASA’s SuomiNPP satellite on December 14, 2020
Image: NASA

Figure 2
Credit: NASA, with data from the British Oceanographic Data
Center’s General Bathymetric Chart of the Oceans

During December 2020, A68a started changing its
direction as ocean surface currents, steered by sea floor
bathymetry, diverted it in a southeasterly direction awayfrom the island. On December 17, a glancing collision withthe shelf broke off a corner off A68a as shown in figure 3.
ESA’s Sentinel‑1 satellites followed the subsequent demiseof A68a through their radar sensors, which are able toimage through cloud. An image acquired on January 31,
2021 appears on the front cover of this issue. Figure 4,
acquired the following day (reproduced overleaf) shows all
the major units of the now disintegrated A68a [2].
References
1		 Breakup of the Larsen Ice Shelves, GEOQ 56, p 9.
2		 The A-68a story		http://www.esa.int/Applications/Observing_the_Earth/The_A-68_story

Figure 3
NASA’s Aqua satellite captured this scene on December 22 with
A68a and the tiny A68d moving away from South Georgia.
Credit: NASA Worldwide Snapshots

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Figure 4 - The disintegrated fragments of tabular iceberg A68a were imaged by the Copernicus-1 mission on February 1, 2021.
Image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO

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This NOAA 18 APT image captured by André T’Kindt at 20:02 UT on February 18 this year shows the two Atlantic
depressions that brought an end to the prolonged spell of freezing weather in nations bordering the North Sea.

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Cloud-free Iceland
European Space Agency

On August 14, 2020, theCopernicus Sentinel-3
mission showed us arare, cloud-free view of
Iceland.
The large, white area
visible on the island
is a national parkthat encompasses the
Vatnajökull Glacier.
Covering an area ofaround 8400 square
kilometres, and with anaverage ice thickness ofmore than 900 metres,
Vatnajökull is not onlyclassified as the biggest
glacier in Iceland, but
the biggest in Europe.
The white, circular patchin the centre of thecountry is Hofsjökull,
the country’s thirdlargest glacier and its
largest active volcano.
The elongated whitearea west of Hofsjökull
is Langjökull, Iceland’s
second largest ice cap.
Reykjavík, the capitaland largest city of
Iceland, is located on the
Seltjarnarnes Peninsula,in southwest Iceland. In
the top-left of the image,several sea ice swirls canbe seen off the coast ofGreenland.
Sentinel-3 is a twosatellite mission to
supply the coverage anddata delivery needed forEurope’s Copernicus
environmental
monitoring programme.
Each satellite’s
instrument package
includes an opticalsensor to monitorchanges in the colour ofEarth’s surfaces.

The Sentinel-3 missing acquired this image of Iceland on August 14 last year
Credit: image contains modified Copernicus Sentinel data (2020),
Processed by ESA, CC BY-SA 3.0 IGO

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Water in the Etosha Pan
MODIS Image of the Day

This false colour MODIS image of the Etosha Pan, was acquired on February 19 by NASA’s Terra satellite.
Credit: MODIS Land Rapid Response Team, NASA GSFC

The Etosha Pan in northern Namibia has been called an‘ephemeral wonder’. For much of the year the large salt
pan is bone dry, and winds pick up its dust and salt andspread it across the arid landscape. But in years when thewet season brings abundant rains, the large, shallow basinstands out as a temporary oasis.
After an extended dry season, rains came to the region inearly 2021, filling streams and rivers with enough water toreach the inland salt pan. According to news reports, partsof northeastern, central, and southern parts of Namibia
saw rainfall double or triple the norm in January 2021. This
followed a wet December, which brought about 25% morerain than normal. As of February 7, the wet season rainfall
total was the highest since 2010 and 2011.
The Moderate Resolution Imaging Spectroradiometer(MODIS) on NASA’s Terra satellite acquired this false-colour image of the Etosha pan on February 19. 2021.
The image combines visible and near-infrared light(bands1,4,3) such that vegetation appears bright green
and water is teal. Mineral salts appear white, except where
they are moistened with water and may thus appear grayor light teal. Unvegetated land appears tan and high cloud,which contains ice or moisture, may be tinted with teal.
The Etosha Pan measures roughly 130 by 50 kilometres,
though it is quite shallow. The basin is connected tohundreds of small streams and channels that start inAngola, but it takes a substantial amount of rain for water
to move far enough through the system (seeping into
the riverbeds along the way) to fill the pan. The mostprominent tributary is the Ekuma River. Once that water
arrives, the area becomes a haven for flamingos, pelicans,and other birds, as well as rhinos and impala.

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