Gaofen 3

Long name	Gaofen 3
Short name	GF3
Sensor type	Synthetic-aperture radar (SAR)
Platform	GF3
Frequency	5.4 GHz
Band (wavelength)	C (5.5 cm)
Polarization	Single, dual, quad
Key file name (use to open data set)	*.meta.xml
Supported file name extensions	*.xml
Data distributor	People's Republic of China, Commission of Science, Technology and Industry for National Defense (COSTIND)
Sections	Data product name and description Distribution disk files Returned data for supported format References

Data product name and description

Gaofen 3 (GF3) is the first C- band high-resolution SAR satellite with a meter-level resolution from China. GF3 carries a SAR imager operating in C-band, capable of providing Earth images up to 1-meter resolution (with 10-kilometer ground swath).

The GF3 SAR package can operate in 12 different working modes, from high-resolution (1 m) to large-swatch (650 km), and from maritime imaging to combined land and water imaging. GF3 covers the globe with an all-weather, 24-hour observation service with 12 imaging modes. GF3 has a spatial resolution ranging from one meter through 500 m, and its largest viewing swath is 650 km.

GF3 has the following acquisition modes:

Spotlight
Stripmap
ScanSAR
Wave

The acquisition modes are further divided into 12 observation modes summarized in the following table.

Note: The information provided herein is based on the data distributor's documentation cited under References.

Mode	Swath width (km)	Resolution (range x azimuth, m)*	Polarization	Description/notes
Spotlight [SL]	10	0.9 to 2.5 x 1.0 to 1.5	Single (HH or VV)	Incidence angles range from 20 through 50 degrees.
Ultra-fine stripmap [UFS]	30	2.5 to 5 x 3	Single (HH or VV)	Incidence angles range from 20 through to 50 degrees.
Fine stripmap [FSI]	50	4 to 6 x 5	Dual (HH or VV)	Incidence angles range from 19 through 50 degrees.
Wide fine stripmap [FSII]	100	8 to 12 x 10	Dual (HH and HV or VV and VH)	Incidence angles range from 19 through 50 degrees.
Standard stripmap [SS]	130	15 to 30 x 25	Dual (HH and HV or VV and VH)	Incidence angles range from 17 through 50 degrees.
Narrow ScanSAR [NSC]	300	30 to 60 x 50 to 60	Dual (HH and HV or VV and VH)	Incidence angles range from 17 through 50 degrees.
Wide ScanSAR [WSC]	500	50 to 110 x 100	Dual (HH and HV or VV and VH)	Incidence angles range from 17 through 50 degrees.
Global observation [GLO]	650	350 to 700 x 500	Dual (HH and HV or VV and VH)	Incidence angles range from 17 through 53 degrees.
Quad-pol stripmap [QPSI]	30	6 to 9 x 8	Quad (HH and HV and VV and VH)	Incidence angles range from 20 through 41 degrees.
Wide quad-pol stripmap [QPSII]	40	15 to 30 x 25	Quad (HH and HV and VV and VH)	Incidence angles range from 20 through 38 degrees.
Wave [WAV]	5 x 5	8 to 12 x 10	Quad (HH and HV and VV and HV)	Incidence angles range from 20 through 41 degrees.
Extended incidence angle [EXT]	130 (EL) 80 (EH)	15 to 30 x 25	Dual (HH and HV or VV and VH)	Extended low-incidence angles range from 10 through 20 degrees. Extended high-incidence angles range from 50 through to 60 degrees.

* Resolution is always single-look complex (SLC) unless noted otherwise.

GF3 has the following product levels:

Level 1A
Level 1B
Level 2

Processing level	Acquisition mode	Description/notes
1A Single-look complex (SLC)		Complex data retaining the amplitude and phase information. Slant-range geometry.
1B Single-look image products (SLP)		Detected data in amplitude. Slant range geometry.
1B Multi-look image products (MLP)		Detected data in amplitude. Ground range geometry.
2 Geocoded products (SGC)		Map projection.

CATALYST Professional supports Level 1A SLC data with an associated RPC model for the following observation modes:

Spotlight [SL]
Ultra-fine stripmap [UFS]
Fine stripmap [FSI]
Wide fine stripmap [FSII]
Quad-pol stripmap [QPSI]
Wide quad-pol stripmap [QPSII]
Wave [WAV]

Distribution disk files

A GF3 data set is organized in a specific folder structure on disk. GDB uses this folder structure and the file names to identify the data product type.

Warning: Data sets for this sensor are organized in a specific folder structure on disk. GDB uses this structure and the file names to identify the data product type. Do not alter the folder structure or any file names prior to data ingestion to ensure the image data and auxiliary information are imported correctly.

You can open a GF3 data set by selecting the *.meta.xml file.

If an incidence.xml file exists, you will be prompted to load with calibrations, as follows:

:Calibration Type:Sigma Nought
:Calibration Type:Gamma Nought
:Calibration Type:Beta Nought
:Calibration Type:None

With CATALYST Professional EASI, Python, or a text-based application, the format of the input file name can be similar to the following:

GF3_SAY_FSI_004800_E116.3_N40.1_20170708_L1A_HHHV_L10002468626.meta.xml:Calibration Type:Sigma Nought
GF3_SAY_FSI_004800_E116.3_N40.1_20170708_L1A_HHHV_L10002468626.meta.xml:Calibration Type:None

GF3 satellite data is distributed in a a multi-file structure, including imagery, metadata, and lookup tables in separate files as described in the following table.

File name	Format	Required	Contents/details
GF3_*.meta.xml	Extensible Markup Language (XML)	Yes	Key file name, contains data set metadata
GF3_.incidence.xml GF3__Strip_X.incidence.xml	Extensible Markup Language (XML)	Yes	Incidence angle data
GF3_.tiff GF3__Strip_X.tiff	GeoTIFF	Yes	Image data
GF3_.rpc GF3__Strip_X.rpc	Text	Optional	Rational function data
GF3_*.thumb.jpg	Joint Photographic Experts Group (JPEG)	Optional	Thumbnail file
GF3_*.jpg	Joint Photographic Experts Group (JPEG)	Optional	Overview file

Returned data for supported format

GF3 data can be opened directly in its raw vendor format or imported into a PCIDSK (*.pix) file using the key file name (*.meta.xml). For optimal processing, use the PCIDSK format.

The following table describes the data structure after it is opened by GDB.

Data product	Data returned	Details
FSI_SLC (L1A) FSII_SLC (L1A)	2 x [C32R] raster channels (HH/HV complex) 1 x [ORB] orbit segment 1 x [BIN] rational function model 1 x [ARR] incidence angle array	If calibration is not applied, image data will be type C16S.
QPSI_SLC(L1A) QPSII_SLC (L1A) WAV_SLC (L1A)	4 x [C32R] raster channels (HH/HV/VH/VV complex) 1 x [ORB] orbit segment 1 x [BIN] rational function model 1 x [ARR] incidence angle array	If calibration is not applied, image data will be type C16S.
SL_SLC (L1A)	1 x [C32R] raster channel (HH or VV complex) 1 x [ORB] orbit segment 1 x [BIN] rational function model 1 x [ARR] incidence angle array
UFS_SLC(L1A)	1 x [C16S] raster channel (HH/HV detected) 1 x [ORB] orbit segment 1 x [BIN] rational function model 1 x [ARR] incidence angle array

References

GF3 Satellite Product User Manual. China Resources Satellite Application Center: December, 2006.