What better way to celebrate nearly two months on orbit than with the first image captured by TshepisoSat that shows the earth from space. What makes the image even more special is that, as mentioned before, the satellite is not stabilised in three-axes. Images are captured without any control of where the camera is pointing and so far images have either been of empty space or the sun.
The satellite was commanded from the ground station to switch on its camera and capture the image. The image was then transferred to the on-board storage and the camera turned off. The image was then downloaded from the satellite to the ground station.
South Africa as seen by TshepisoSat – Original image
The camera on TshepisoSat was added as an additional “nice to have” next to the main payload beacon transmitter. It is also to be used to monitor the deployment of the payload beacon transmitter antenna.
Out of curiosity the original image captured by TshepisoSat was sent to Dr Ingrid Stengel from NamibGeoVista GeoConsult & Imaging in Windhoek, Namibia to see what can be learnt from the image. Even though the image is of very low-resolution compared to commercial images, this is what she had to say:
Overview
The visual image captured by ZACUBE-1 on 14 Jan 2014 covers large portions of southwestern South Africa, as well as southern Namibia and southernmost Botswana.
Due to the oblique inclination, the spatial resolution of the image is best in the southwestern part of the subcontinent and decreases towards the north and northeast, so that the surface area is strongly condensed there. The earth curvature is just about visible in the northeastern-most corner.
The original image has a strong dominance of magenta and blue colours, not unlike the early Landsat images with their limited spectral properties. However, with suitable user-defined contrast stretching, even data of such limited pixel size and spectral range can reveal a host of regional information.
Clouds and fog
Most of the Western and Northern Cape is cloudfree. Towards the north, dense coastal fog is visible along the Atlantic Coast of the Richtersveld and southwestern Namibia. A couple of small dark patches between the fog and the Namibian coastline (where blue ocean water shines through) indicate that a notable land-sea breeze was present which locally pushed the fog back seaward.
Over the southern Namibian escarpment highlands (Huib High Plateau), an enormous, well-defined cumulonimbus cloud has developed. Even the cloud shadow is visible along the southwestern rim of this feature.
Else, seasonal cloud development is limited to southern Botswana and towards Mpumalanga (northeastern corner of the image). The overall synoptic pattern behind this largely cloud-free situation is the aftermath of a high pressure system (cold front) which had moved onto southwestern Africa from the Atlantic, in a west-easterly direction, during 7/8/9 Jan 2014. The cold air had pushed the normally prevailing tropical air masses with their high moisture content back eastward, even for a couple of days.
Land cover
This cloud-free scenario allows for a stunning view of the Northern and Western Cape as well as of southern Namibia.
In Namibia, the coastal Namib Desert (light colours), the Namibian Great Escarpment, and finally the southern plateaus consisting of dark-looking Nama and Karoo rocks are visible. Further inland (eastward), lighter coloured Kalahari dune fields are represented in beige-pink colours (just before the cloud cover starts over southern Botswana).
Moving south, the Great Escarpment of South Africa, including the Cape Fold Mountain belt with its numerous narrow mountain ranges, is clearly visible. In the Northern Cape, the landscape boundary between the dark green, narrow Escarpment and the pale, reddish-beige Karoo is most prominent. Towards the interior of the Northern Cape, the narrow, green ribbon of irrigation-based agriculture along the Orange River (approx. between Douglas and Upington) can clearly be discerned.
Further south, both the Groot Karoo and the Klein Karoo plains are mostly green. Elongated pale to white areas in the Groot Karoo represent large pans and ancient drainage systems (proto Orange river and others).
The intensive agriculture in the coastal plains and basins of the Western Cape results in less lush, slightly beige colours.
Much of the southern coastline is highlighted by a white rim which represents the combined spectral signal of sandy beaches and adjacent zones of ocean breakers.
Ocean information
By applying specific contrast stretching it is possible to visualize low cloud streets over the coastal waters of the Indian and Atlantic ocean, as well as presumed colour differences in the ocean currents themselves. In addition, a major sediment spill from the mouth of the Gourits River, southwest of Mossel Bay can be detected, which extends from the coast in a southwesterly direction far into the Agulhas current.
Some of the images manipulated by Dr Stengel can be seen below (keeping in mind the low-resolution nature of the original image):
001 General contrast enhancement (Photoshop).
002 Contrast-stretched enhancement for land cover (Envi)
003 Contrast stretch to enhance features in the ocean.
004 High-pass filtered and contrast-enhanced, to sharpen
the image.
The French South African Institute of Technology would like to thank Dr Ingrid Stengel from NamibGeoVista GeoConsult & Imaging for her contribution in analysing the image.