Visible Imagery

Incoming solar radiation is reflected by the Earth’s surface or cloud and bounces back out to space where it is detected by the satellite. The images produced show the albedo (how good a surface is at reflecting light) of the surface.  For example, snow will appear brighter than grass and thicker clouds are brighter than thin clouds.

On MetFlight, one image is available each hour. The major advantage of visible imagery is that you can see where the clouds actually are. This should help when you read an ARFOR. If the ARFOR says “AREAS BKN CUSC 2000 TOPS 5000”, you don’t really know where the “AREAS BKN” are. Is there cloud on the pass I want to fly through? By taking a look at the most recent visible satellite image you will be able to answer this question. Of course, by the time you get there the situation will probably have changed! Using a loop of a series of visible satellite images will help determine if areas of cloud are dissipating or growing. 

You can also gather information about the type of cloud. Stratiform cloud appears smooth, while cumuliform appears lumpy.

Remember, these images tell you nothing about cloud bases or tops — you need to look at other information, such as METARs, TAFs and ARFORs for this information.

The major limitation of visible satellite imagery is that it is available only during daylight hours. 

Let's work through an example.

In the image on the right, dark areas are cloud free. There is a solid area of cloud in the western Bay of Plenty, you can see it along the eastern side of the Kaimai Range. There is also cloud around Taranaki, although there appears to be breaks in it. Cloud is also along the South Island West Coast, but there are gaps in the cloud in northern Westland and Buller. Most of the east of the South Island is cloud free. 

The red arrow indicates an area of very smooth looking cloud. This is stratus. We can’t be totally sure of that from the satellite image, so other information is needed. In this case, the Christchurch METAR reported BKN008. It would also be worthwhile looking at the Kaikoura cloud base. 

The yellow arrow indicates an area of cirrus, although we can’t be sure of that from this image alone either. We can, however, tell there is cloud in the area and that it’s thin enough to see the ground below. The Dunedin METAR may help, but the infrared satellite image is the real key in this case (bottom image).

Invercargill

Above mean sea level

TCu

Towering Cumulus

agl

above ground level

Cb

Cumulonimbus

Flight Information Service communications

ATS

Air Traffic Service

Royal New Zealand Air Force

in vicinity of aerodrome Thunderstorm

ATC

Air Traffic Control

VC

in vicinity of aerodrome

Probabilityxx%

TIL

Until

FM

From

Becoming

Temporarily

Routine air report from aircraft in flight

FIR

Flight Information Region

Internet Flight Information Service

VFR

Visual flight rules

Automatic Terminal Information Service

BWR

Basic weather report

New Zealand Flight Information Region

Aerodrome special routine meteorological report

Automatic aerodrome routine meteorological report

Aerodrome routine meteorological report

TAF

Aerodrome forecast

Area forecast

Significant meteorological information