Calculate Normalized Difference Snow Index (NDSI)

[RobinGummels]

Description:
Implement Step 6: Calculate the Normalized Difference Snow Index using the formula NDSI = (B03 - B11) / (B03 + B11) for the median composite.

Tasks:

• Implement NDSI formula: (B03 - B11) / (B03 + B11)
• Handle division by zero cases
• Ensure NDSI values are in range [-1, 1]
• Create visualization of NDSI result
• Validate against known glacier locations from seeds

Acceptance Criteria:

• NDSI is correctly calculated for all pixels
• No NaN or Inf values from division issues
• NDSI values are within valid range [-1, 1]
• High NDSI values (>0.42) correspond to seed locations