# Products and bands

Every product is a GeoTIFF, described in Python by a small metadata record. The record holds the product's identity, such as burst, date and type, and [FileManager.get_product_path()](../reference/filemanager.FileManager.md#s1bursts.filemanager.FileManager.get_product_path) turns it into the file's location. This page describes what the files contain.


# Burst products

Each burst product is one GeoTIFF, with its bands named in the band descriptions:

| Product | Bands | Values |
|----|----|----|
| RTC backscatter | `gamma0`, `scattering_area` | `gamma0` in linear power, `scattering_area` without units |
| GTC backscatter | `beta0` | Linear power |
| Coherence | `coherence` | Magnitude, 0 to 1, without units |

Backscatter is stored as linear power, not decibels, in products and composites alike. Convert with `10 * log10(value)` only after averaging, since the mean of decibels is not the decibel of the mean. The `scattering_area` band describes how much ground each pixel covers. [Local resolution weighting](resolution-weighting.md) explains how composites use it.


# Composites

A composite has one band, the quantity of its inputs: gamma-0, beta-0 or coherence, in the same units. Its band description is the polarization, such as `VV`. The bands of the quality layers are named `num_obs` and `cqm`.

With `write_qa=True`, each quality layer of a composite is written to a file of its own:

- The number of observations (`QA-NUM`) counts the acquisitions that contributed to each pixel.
- The composite quality map (`QA-CQM`) rates how fine the combined detail of each pixel is, without units. Only LRW composites have it.

[Local resolution weighting](resolution-weighting.md#the-quality-layers) explains both.


# Missing values

Pixels without a value are `NaN`, for example outside the burst. Keep them missing in statistics and plots rather than replacing them with zero. The one exception is the number of observations, an integer layer that marks pixels without data as 0. Both are declared as the file's no-data value, so `src.read(1, masked=True)` masks them.


# Metadata tags

Each GeoTIFF also has tags that say how to read it and how it was made. They include the units of the stored values, the acquisition dates, every processing setting, such as the DEM, the resampling or whether the topographic phase was removed, and the SNAP and s1bursts versions:

``` python
with fm.open(product) as src:
    print(src.descriptions, src.units)
    print(src.tags())
```

These tags make a file understandable on its own, even when separated from the code that wrote it. A composite records the processing settings of its inputs, which must all match. A resolution-weighted coherence composite records those of its coherence products, not of the RTC products that weight them. Where the [CEOS-ARD SAR specification](https://ceos.org/ard/) has a term, the tag names use it, so it can be looked up there. s1bursts borrows the vocabulary only and does not claim conformance with the specification.


# Filenames

A filename contains only what distinguishes one product from another, in fixed fields separated by `_`. Each product type has its own pattern:

| Product | Filename pattern |
|----|----|
| SLC burst | `S1_SLC_<orbit><pass>_<burst>_<swath>_<pol>_<date>.zip` |
| RTC backscatter | `S1_RTC_<orbit><pass>_<burst>_<swath>_<pol>_<date>_<zone>.tif` |
| GTC backscatter | `S1_GTC_<orbit><pass>_<burst>_<swath>_<pol>_<date>_<zone>.tif` |
| Coherence | `S1_COH<baseline>_<orbit><pass>_<burst>_<swath>_<pol>_<date1>_<date2>_<zone>.tif` |
| RTC LRW composite | `S1_RTC_LRW[_<qa>]_<square>_<pol>_<start>_<end>.tif` |
| Coherence LRW composite | `S1_COH<baseline>_LRW[_<qa>]_<square>_<pol>_<start>_<end>.tif` |
| RTC or GTC pass composite | `S1_RTC_COMP_<pass>[_QA-NUM]_<square>_<pol>_<start>_<end>.tif`, with `GTC` for GTC |
| Coherence pass composite | `S1_COH<baseline>_COMP_<pass>[_QA-NUM]_<square>_<pol>_<start>_<end>.tif` |

The part in square brackets appears only in the name of a quality layer. The fields are:

| Field | Meaning | Example |
|----|----|----|
| `<orbit>` | Relative orbit number, three digits | `015` |
| `<pass>` | Pass direction: `A` ascending, `D` descending | `A` |
| `<burst>` | ESA burst ID, six digits | `030346` |
| `<swath>` | Sub-swath | `IW1` |
| `<pol>` | Polarization | `VV` |
| `<date>` | Acquisition date, `YYYYMMDD` | `20220801` |
| `<date1>`, `<date2>` | Dates of the primary and secondary acquisitions of a pair | `20220801`, `20220813` |
| `<baseline>` | Days between the acquisitions of a pair, two digits | `12` |
| `<zone>` | UTM zone of the product's CRS | `32N` |
| `<square>` | MGRS grid square | `32TLS40` |
| `<start>`, `<end>` | First and last day of the `time_range`, or of the acquisitions without one | `20250801`, `20250831` |
| `<qa>` | Quality layer: `QA-NUM` or `QA-CQM` | `QA-CQM` |

The RTC product of the [Quickstart](quickstart.md), burst 30346 in sub-swath IW1 on ascending orbit 15, is named `S1_RTC_015A_030346_IW1_VV_20220801_32N.tif`, and the number of observations of an LRW composite is named `S1_RTC_LRW_QA-NUM_32TLS40_VV_20250801_20250831.tif`.

[FileManager](../reference/filemanager.FileManager.md#s1bursts.filemanager.FileManager) keeps SLC bursts in `s1-slc`, burst products in `s1-prod` and composites in `s1-comp`, below the directory it is given.

Processing settings are not part of the name. They are recorded in the tags instead, and a rerun compares them before it skips an existing file. See [Reprocessing and failures](processing.md#reprocessing-and-failures).