29 votes

Why clouds are not moving in NASA's video of the Moon passing in front of the Earth?

The clouds can be seen moving but of course it's subtle at first glance. Frame 16: Frame 20:
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27 votes
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Why clouds are not moving in NASA's video of the Moon passing in front of the Earth?

They are moving, but not fast enough to notice at the distance shown. From the NASA page: These images were taken between 3:50 p.m. and 8:45 p.m. EDT on July 16, showing the moon moving over the ...
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  • 11.1k
23 votes
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How is ocean salinity measured from space?

In a nutshell: The instrument measures microwave radiances (after calibration) If we know the sea surface temperature, we can use radiances to calculate emissivity. The emissivity at 1.4 GHz is ...
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  • 11.1k
13 votes
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How does remote sensing of ocean currents work?

I'm not familiar with land-based methods, but for global measurements, one method is to use satellite altimetry (I'm more familiar with the geodesy side, but many of the same satellites are used). I ...
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  • 1,276
13 votes
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What color is the Sahara desert, as seen from orbit?

Neither. The Sahara Desert is heterogenous. It’s yellow, red, orange, brown, black, and even green in certain places and at certain times of year. Slightly less cheeky answer: neither. Both examples ...
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12 votes

What color is the Sahara desert, as seen from orbit?

Remember from school when you learned that light is actually photons oscillating at specific frequencies, and we happen to perceive some of these frequencies as specific colors? Technically, ...
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  • 419
11 votes

Why clouds are not moving in NASA's video of the Moon passing in front of the Earth?

The image is real, and the clouds are moving, they just move slow, as clouds do. The unnatural appearance arise because they are taken by DSCOVR at an extraordinarily large distance, from a place ...
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10 votes

To what accuracy and precision do we know the volume of the Earth?

One way to approach this is to treat the Earth as an oblate ellipsoid. This would mean the errors arise from the uncertainties in the Earth's equatorial radius and the flattening. From Groten, "...
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  • 20.2k
10 votes
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Locating Missing Airplanes using Remote-Sensing Satellites

Civilian earth observing SAR satellites do not always operate over empty swaths of oceans (specially in the middle of Indian Ocean) in order to save power. They are not designed to track a fast moving ...
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  • 2,361
10 votes

How do the pros measure humidity?

The WMO report Instruments and Methods of Observation has a chapter on Measurement of humidity and a separate chapter on Measurement of upper-air pressure, temperature, humidity. The first deals with ...
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  • 772
9 votes
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TRMM rainfall measurement for synoptic systems

The Tropical Rainfall Measuring Mission (TRMM) satellite is a single satellite, carrying multiple instruments on board, as described here. It makes a total of 16 orbits/day at a low altitude of 400 km,...
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  • 4,925
8 votes
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What sort of instruments do planetary geologists use to predict that there are oceans on the moons Titan and Europa?

As casey said, the satellite isn't an instrument in itself, it is a platform hosting many instruments. What you're talking about the discovery of oceans on Titan and Europa, you're referring to the ...
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  • 924
8 votes
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What are the advantages in looking at an OLR map versus looking at IR satellite imagery?

First OLR map is usually graded in flux units (W/m2) thus it is quantitative data, not just a visual picture. Clouds themselves are not a very reliable indicator of high convection and thunderstorm ...
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8 votes
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How do weather services measure wind

Weather stations and airports around the world almost always include an anemometer. Because of ground friction, the wind speed varies with height, so instrumental deployment is set at a standard ...
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8 votes
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Odd Inuksuk-like objects

I can engage in some educated speculation about what you think you see, but I'm confident you were fooled by the shadows in the image, which are caused by a low sun angle and distorted by the terrain. ...
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  • 3,038
8 votes
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Public sources of topographical data of Earth?

This is an interesting and common question, so I'll try to give a good answer here, that I think is a good place, as well as GIS and Open Data SE. First, regarding the format, you will never find data ...
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7 votes
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Predicting earthquakes using disturbances in DTH TV transmission

Earthquake prediction have been discussed before in this forum and is rather dispiriting. Distortion in transmitted signals could be an early indication of earthquake, but seismometers (geophones) are ...
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  • 5,896
7 votes

To what accuracy and precision do we know the volume of the Earth?

Talking about the volume of the Earth, we have to ignore that it is not static but in fact highly dynamic. The tides alone make the height differ by up to 50 cm. The information I take is from a 2003 ...
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7 votes
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How to remove 'silk braid' noise in satellite data?

You ask, How to remove these abnormal value for more precise data? The short answer is that you might be able to make your data look more representative of the natural 'truth', but you will probably ...
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  • 10.7k
7 votes
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How do optical satellites detect different leaf types?

Short answer Different plants reflect light at different wavelengths with specific patterns. If you know the reflection pattern of a broad-leaved forest and that of a needle-leaved forest, you can ...
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7 votes

How to convert mol/m^2 to total mass ( e.g gram, kg etc )?

$\rm \frac{mol}{m^2}$ shows the amount of $\rm{NO_2}$ in the atmosphere over a square meter of surface area - in mols. The molar mass of the $\rm{NO_2}$ is $14+2\cdot 16=46$. It means, the mass of 1 ...
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  • 642
7 votes

How do I convert Sentinel-5p / TROPOMI vertical column density to concentration?

The unit mole / m² has dimensions count per area; the unit µg / m³ has dimensions mass per volume. To go from a quantity per area to a quantity per volume, you need to understand some properties of ...
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  • 11.1k
7 votes
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Remote sensing of glaciers, season for data collection

Looking around at some random articles, for example Karpilo 2009, Geissler et al 2021, Litt et al. 2019, and Racoviteanu et al 2008 my impression is that researchers primarily use images of the ...
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  • 10.7k
6 votes

What geophysical instruments should I use to detect water without drilling?

Hydrosource Associates (no personal relation) claims to use the following: HSA’s use of geophysical instruments and methods includes seismic, electrical resistivity, ground penetrating radar, ...
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  • 2,688
6 votes
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What geophysical instruments should I use to detect water without drilling?

From what @Richard and @JoeKington said in their answers, it seems that the usual way of finding water is through a hydrological map. However, for the sake of completeness, I'll include here a bit ...
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  • 843
6 votes

How does remote sensing of ocean currents work?

Joe Kington has provided an excellent answer re sensing from space. Torbjørn T. pointed out in a comment that the site that I linked for context actually has a good explanation... so after blushing ...
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6 votes
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Need help understanding this satellite image of Larson C ice shelf

I found a natural-color image of the same area: 68.28 South, 60.47 East, North is up, resolution is 130m/px, which makes the whole image about 100 km x 100 km. Looking at the image i'd say that: sea ...
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  • 176
6 votes
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The giant 6,000 km$^2$ iceberg A-68; will ground-truth telemetry supplement satellite tracking data?

I can't imagine a moving object more suitable for remote sensing tracking than Iceberg A-68, with such slow displacement and huge size. So I don't think it will be particularly useful to install any ...
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6 votes
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How does ice-penetrating radar "see" through kilometers of ice without being absorbed?

Water molecules do interact with microwaves and in microwave ovens that operate at 900MHZ- 2.5GHz. This Radar instrument operates using Very High Freq Radio Waves at 193MHz [1]. At lower-than-...
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6 votes

How do the pros measure humidity?

We use something like an Onset HOBO electronic sensor. They've got logging (and in some cases, networking) built in. They'll typically log both temperature and relative humidity at regular intervals ...
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