mfkiwl/fy-2x_clut

Add colour to your FY-2x images using CLUT.

Introduction

The Fengyun-2 series of satellites are geostationary satellites that deliver images of earth once per hour. The delivery consists of S-VISSR data: 1 VIS, 3 IR and 1 Watervapour images. They are delivered on the L-band frequency 1687.5 MHz. If you are within the footprint of the satellite, it is possible to receive with at least a 1.2m dish and Nooelec Saw filter. As there are both VIS and IR channels, it is possible to create false colour images by using CLUT (colour look up table).

Image data

Below are the following images and their resolutions delivered by the satellite.

Image data resolutions

Channel	Type	Resolution
FY-2x_1	IR	2291 x 2501
FY-2x_2	IR	2291 x 2501
FY-2x_3	WV	2291 x 2501
FY-2x_4	IR	2291 x 2501
FY-2x_5	VIS	9160 x 10004

Requirements

To use the CLUT requires the following:

Name	For	Author	Source
Decoder	Decodes the S-VISSR data	@aang254	https://github.com/altillimity/S-VISSR-Ingestor
GeoSatSignal	Applies the CLUT from a file	David Taylor	https://www.satsignal.eu/software/geosatsignal.htm

Instructions

Hardware requirements

You can use a 1.2m or larger dish. The feed skew needs to be set accordingly depending on location. For example in Japan, I need to set the feed skew to 45 degrees. I use a patch antenna (shown) as it gives good dish illumination.

You need to rotate the feed to set the correct skew.

I use Nooelec Sawbird and SPF5189Z LNA for extra gain (if you need it). I don't think the bias tee output on the Airspy can output enough current to power both LNAs, so you would need to use external +5V supply. I use 4 x NiMH batteries.

Check signal in SDRSharp

The signal in SDRSharp is a 1 MHz wide signal and you need to get at least 10 dB SNR for an 100% error free image:

Run the decoder

Use the decoder to get the images by visiting the link above (instructions to use are on the site).

Invert and Upscale the IR (FY-2x_1)

Open the IR image in your image editor eg. GIMP and invert the image colour so the clouds appear white. In addition the IR image needs to match the pixel size for the visible. In your image editor, upscale the IR to 9160 x 10004 and save as IR.bmp. Open the visible FY-2x_5 image and re-save to VIS.bmp file as GeoSatSignal needs both of the files to be .bmp

Download Geosatsignal

Download the Geosatsignal software from the above link.

Download the CLUT (colour look up table)

Download the CLUT above (.bmp) and copy it in GeoSatSignal folder below:

"Tools\SatSignal\GeoSatSignal"

To use the CLUT you need to activate it in "Vis Ch." Set the "Brightness" and "Crispen" to "None". Also set the output file as ".TGA".

Settings

In GeoSatSignal, to apply the CLUT correctly requires correct adjustment. Goto "Options" and "Common setup". Under "WEFAX thermal calibration", use the below values:

Setting	Gain	Offset
Cloud cyan top	150	0
Cloud white top	70	50

Input the VIS.bmp and IR.bmp files into GeoSatSignal

Drag and drop one of the files into the corresponding box (e.g. visible for VIS) Then save as 1:1 size.

Example images

Full disk

Australia

Saudi Arabia

Use with EWS-G1

Since the EWS-G1 has an IR channel, in theory the above file can be used here. Although you need to play with the settings to get the best results. Since I cannot receive this satellite, I cannot verify this.

Credits

Thanks to @aang254 for his decoder for FY-2x satellites and David Taylor for GeoSatSignal program.