Less data from Sentinel 1B

Question

I am trying to access Sentinel 1 data from Google Earth Engine. For my study area which is a part of the Himalayan region I am getting only few data from Sentinel 1B for the year 2019 and I am not getting any data from 1B for the year 2018. Shouldn’t we be getting equal number of data from both 1A and 1B. It would be really helpful if some one could explain the reason behind it.

//Importing Area of Interest
var kullu = ee.FeatureCollection("projects/ee-rchandraprabha15/assets/kullu");
kullu = kullu.geometry();
var start_date = '2019-01-01';
var end_date = '2019-12-31';

// Filter the collection for the VH and VV product from the 1A descending track
var collection = ee.ImageCollection('COPERNICUS/S1_GRD')
     .filterDate(start_date, end_date)
     .filter(ee.Filter.eq('instrumentMode', 'IW'))
     .filterMetadata('transmitterReceiverPolarisation', 'equals', ['VV', 'VH'])
     .filterBounds(kullu).map(function(ig){
     return ig.clip(kullu);
  
});
// List the platform and the no.of images
var orbits = ee.Dictionary(collection.aggregate_histogram('platform_number'));
print('List of platform number', orbits); // Check in console

Output:

For the year 2019: List of platform number: Object (2 properties) A:148 B:11

As you can see there are only 11 images from 1B for a whole year in my study region.

When considering Ascending and Descending orbits for the year 2019, List of orbitProperties_pass Object (2 properties) ASCENDING: 122 DESCENDING: 37

Why is there uneven distribution of data?

Here is the link to the code: https://code.earthengine.google.com/82cabcff67482fc7bde6ccae526784df

Answer 1

The Sentinel-1 observation scenario shows your where and how the earth is imaged with the S1 pair.

https://sentinels.copernicus.eu/web/sentinel/missions/sentinel-1/observation-scenario

As you can see, your AOI is usually covered by only one satellite, so you'll get much more results

The image above refers to a specific time frame. The overall scenario is the same (pre S1B malfunction), with small changes based on maintenance or global events that require more coverage.