Alaska Satellite Facility - Distributed Active Archive Center


Seasat – Technical Challenges – 8. Focusing Challenges

In modern systems, synthetic aperture radar (SAR) echoes are sampled in a complex fashion using IQ-demodulation. The I and Q components are samples of the same signal that are taken 90 degrees out of phase. Separating I and Q in this way allows measurement of the relative phase of the components of the signal, and is a requirement for the SAR focusing algorithm. The Seasat platform used an older method to sample echoes, storing real (not complex) returns in offset video format.

Seasat – Technical Challenges – 4. Data Cleaning (Part 2)

4.3 After development of each of the software pieces described previously in this section, the entire data cleaning process was driven by the program This procedure was run on all of the swaths that were output from SyncPrep to create the first version of the ASF online Seasat raw data archive (the fixed_ …

Seasat – Technical Challenges – 4. Data Cleaning (Part 2) Read More »

Seasat – Technical Challenges – 2. Decoder Development

Starting in the summer of 2012, ASF undertook the significant challenge of developing a Seasat telemetry decoder in order to create raw data files suitable for focusing by a synthetic aperture radar (SAR) correlator. In this case, that means processible by ROI, the Repeat Orbit Interferometry package developed at Jet Propulsion Laboratory. In addition to …

Seasat – Technical Challenges – 2. Decoder Development Read More »

Seasat – Technical Challenges – 3. Decoded Data Analysis

With the Seasat archives decoded into range line format along with an auxiliary header file full of metadata, the next step is to focus the data into synthetic aperture radar (SAR) imagery. Focusing is the transformation of raw signal data into a spatial image. Unfortunately, pervasive bit errors, data drop outs, partial lines, discontinuities and …

Seasat – Technical Challenges – 3. Decoded Data Analysis Read More »

Seasat – Technical Challenges – 10. Quality Issues

After the decoding, cleaning and focusing of the Seasat SAR data, many artifacts still exist in the initial ASF Seasat SAR products. Most of the artifacts observed in the images result from system interferences during data acquisition, missing data as a result of multiple transcriptions between media storage since 1978, and processing decisions implemented in the ASF Seasat Processing System. ASF’s intent is to distribute as much of the historic dataset as possible to our users while offering transparency about known quality issues.