I have to mask all the cloudy pixels, and because the QA info is stored in bits I am trying to decode them using this code. However when I chart the masked timeseries, I get an error: Error generating chart: Data column(s) for axis #0 cannot be of type string. Is this code robust for masking modis cloudy pixels?

var M = ee.ImageCollection("MODIS/006/MOD09GA"),
geometry1 = /* color: #d63000 */ee.Geometry.Point([10.644168108701706, 64.4188479841206]),
single = ee.Image("MODIS/006/MOD09GA/2012_10_11");

 var getQABits = function(single, start, end, newName) {
// Compute the bits we need to extract.
var pattern = 0;
for (var i = start; i <= end; i++) {
   pattern += Math.pow(2, i);
return single.select([0], [newName])

// Select the QA band
var QA = single.select('state_1km');

// Get the cloud_state bits and find cloudy areas.
var cloud = getQABits(QA, 0, 1, 'cloud_state')
                .expression("b(0) == 0 || b(0) == 2 ");

// Get the land_water_flag bits.
var landWaterFlag = getQABits(QA, 3, 5, 'land_water_flag');

// Create a mask that filters out deep ocean and cloudy areas.
//var mask = landWaterFlag.neq(7).and(cloud.not());

var filter = function(image){ 
var mask = landWaterFlag.neq(7).and(cloud.not())
return ee.Image(image).updateMask(mask)

var B1= M.filterDate('2010-04-01', '2014-10-31').select('sur_refl_b01')
var gooddata = B1.map(filter)

 // chart b1 all quality data
 var chartb1 = ui.Chart.image.seriesByRegion({
 imageCollection: B1, 
 regions: geometry1, 
 reducer: ee.Reducer.mean(),
  scale: 1000,
  band: 'sur_refl_b01',

// chart b1 masked quality data
var chartb1mask = ui.Chart.image.seriesByRegion({
imageCollection: gooddata, 
regions: geometry1, 
reducer: ee.Reducer.mean(),
scale: 1000,
band: 'sur_refl_b01',

1 Answer 1


You get an error when charting because you don't have any unmasked data. Your cloud expression is incorrect. According to the data catalog, values that are 0 and 3 are assumed to not be clouds. So your cloud expression should probably be something like this:

b(0) != 0 && b(0) != 3


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