Friday, August 21, 2020

The PO.DAAC is pleased to announce the public release of the CYGNSS Level 1 (L1) Raw Intermediate Frequency (IF) and Full Delay Doppler Map (DDM) datasets from the Delay Doppler Mapping Instrument (DDMI) aboard the CYGNSS satellite constellation.
- CYGNSS Level 1 (L1) Raw Intermediate Frequency (IF) dataset >>
- Full Delay Doppler Map (DDM) dataset >>
The primary CYGNSS instrument, DDMI, measures the incoming radio frequency (RF) streams from three input antenna channels (2 nadir oriented science antennas and one zenith oriented navigation antenna) and processes them in real time into DDMs, which are two-dimensional maps of the signal scattered from the Earth surface as a function of propagation time delay and Doppler frequency shift.

The Raw IF data consist of the raw sensor counts from the DDMI, provided in flat binary format; formatting specifications are available in the guide document. Raw IF is retrieved prior to any digital signal processing, thus providing the highest possible resolution in delay and doppler space allowing for the construction of high resolution DDM data. The Full DDM data, provided in netCDF format, are sampled over a wider range of delay and doppler values compared to the standard DDMs, such as compared with the Level 1 Science Data Record (SDR) or Climate Data Record (CDR); netCDF variable formatting for the Full DDM is explained further in the Data Dictionary. In addition to sampling a wider range of delay and Doppler values, Full DDM processing also retains the uncompressed (lossless) scattered signal strength, as opposed to the compressed DDMs used to produce the SDR and CDR data. The ATBD for these datasets provides greater detail on processing methodology, as well as the science applications for these data.

Discretely processed Raw IF data samples are 30 to 90 seconds in continuous duration (60 seconds is nominal), while the Full DDM data records are typically 10-15 min in sampling duration. The Raw IF and Full DDM processing is initiated by ground commands to the spacecraft coincide with an overpass by one of the spacecraft over a target area of interest. Due to the higher sampling rate of Raw IF, higher spatial resolution compared to standard retrieval methods in the range of 300 meters to 1 km may be achieved; 1km is considered nominal Raw IF resolution. The spatial resolution of Full DDM is comparable to standard L1 CYGNSS data products (i.e., SDR and CDR), yet it provides a higher area of spatial coverage; 25 km is the nominal Full DDM resolution.

The time series for both the Raw IF and Full DDM data is discontinuous and latency is highly variable, as the processing depends on ground-controlled spacecraft commands issued at specific time intervals for a target area of interest on the Earth’s surface. Once CYGNSS spacecraft are operating in Raw IF and Full DDM mode, the latency is comparable to SDR processing (1 to 6 days). More information and access to these data can be obtained directly through the Web Portal via the links in the DOI references below.




Citation: Gleason, S., C. S. Ruf, A. O'Brien, D. S. McKague, "The CYGNSS Level 1 Calibration Algorithm and Error Analysis Based On On-Orbit Measurements", IEEE J. Sel. Topics Appl. Earth Obs. Remote Sens., doi: 10.1109/JSTARS.2018.2832981, 2018.