(1)多通道门控循环单元的土壤温度预测模型

  • 在气象站稀缺地区,相关气象数据难以获取,这使得循环神经网络中长时间序列解释变量的自相关性降低。为解决这一问题,提出基于多通道门控循环单元的土壤温度预测模型。
  • 首先,以门控循环单元(GRU)为基础模块,提取解释变量短期模式特征。这是因为 GRU 能够有效地处理时间序列数据,捕捉短期的动态变化。
  • 其次,为避免较长期解释变量在信息传递过程中引起的模型误差,通过逐渐减小每个 GRU 模型时间步长的方式定义多个辅助网络。这样可以更好地捕获解释变量较长期模式的特征,提高模型对长期趋势的把握能力。
  • 最后,将不同通道捕获的不同时期土壤温度特征相融合。通过融合不同时期的特征,可以增强解释变量的自相关性,使模型能够更准确地建立土壤温度预测值与较长期解释变量之间的变化关系。实验结果表明,该方法在气象信息不易获取时,能有效提高土壤温度预测任务的准确率。

(2)基于四元组损失函数的土壤温度预测模型

  • 传统循环网络模型在预测土壤温度时存在一些问题。直接将解释变量作为输入,并采用均方误差等常用损失函数训练模型,会导致预测模型无法有效提取土壤温度特征,预测结果不具备物理一致性。
  • 为解决这一问题,提出基于四元组损失函数的土壤温度预测模型。该方法将传统损失函数与土壤温度特征之间的距离度量学习相结合,指导预测模型进行训练。
  • 具体来说,将土壤温度数据进行聚类,划分成不同区间并采用不同标签进行区分。通过拉近相同区间内土壤温度特征的距离,推远不同区间土壤温度特征的距离,避免传统循环神经网络模型预测结果不具备物理一致性。实验结果表明,该方法在处理多个解释变量的土壤温度预测任务中具有良好的预测性能。

(3)基于编码器 - 解码器长短期记忆网络的土壤湿度预测模型

  • 相比于土壤温度的预测,土壤湿度受土壤性质、降水和植被等多种因素影响,具有更高的异质性。同时,预测尺度增加会导致未来信息不确定性增强。
  • 为此,提出基于编码器 - 解码器长短期记忆网络的土壤湿度预测模型。编码器将长短期记忆网络(LSTM)作为基础网络,用于编码预测尺度内的特征,增强模型特征提取能力。
  • 通过解码未来信息,并使预测尺度内多个土壤湿度参与损失函数梯度的计算,可以改善未来信息不确定性带来的误差。
  • 将解释变量与解码器的解码信息结合,能够纠正编码器 - 解码器 LSTM 模型的计算偏差。实验结果表明,该方法通过改善未来信息的不确定性,提高了土壤湿度的预测精度。

(4)融合迁移学习的土壤湿度预测时空模型

  • 在预测 SMAP 产品的土壤湿度时,由于数据总量过少,易使深度学习模型出现欠拟合问题。
  • 为解决这一问题,提出融合迁移学习的土壤湿度预测时空模型。该方法利用三维卷积层提取土壤湿度的空间特征,利用 LSTM 模型提取其时间特征,改善传统深度学习模型的预测精度。
  • 采用迁移学习策略,利用具有物理意义的 ERA5 - Land 数据集土壤湿度指导深度学习模型的参数初始化。这样可以避免预测模型出现过拟合,提高模型的泛化能力。实验结果表明,该方法能够有效地提取土壤湿度的时空特征,经过 ERA5 - Land 数据集土壤湿度指导深度学习模型的参数初始化后,改善了深度学习模型预测 SMAP 土壤湿度的预测性能。
% 加载数据
data = load('soil_data.mat');
soilTemperature = data.soilTemperature;
soilMoisture = data.soilMoisture;
explanatoryVariables = data.explanatoryVariables;

% 划分训练集和测试集
trainRatio = 0.7;
numSamples = size(soilTemperature, 1);
numTrainSamples = round(trainRatio * numSamples);
trainIndices = 1:numTrainSamples;
testIndices = numTrainSamples + 1:numSamples;

trainSoilTemperature = soilTemperature(trainIndices, :);
trainSoilMoisture = soilMoisture(trainIndices, :);
trainExplanatoryVariables = explanatoryVariables(trainIndices, :);

testSoilTemperature = soilTemperature(testIndices, :);
testSoilMoisture = soilMoisture(testIndices, :);
testExplanatoryVariables = explanatoryVariables(testIndices, :);

% 基于多通道门控循环单元的土壤温度预测模型
function predictedTemperature = multiChannelGRUModel(explanatoryVariables)
    numChannels = 3;
    gruNetworks = cell(numChannels, 1);
    for channel = 1:numChannels
        gruNetworks{channel} = layergru(100);
    end
    
    timeSteps = [12, 8, 6];
    
    inputLayer = layerinput(size(explanatoryVariables, 2));
    
    channelOutputs = cell(numChannels, 1);
    for channel = 1:numChannels
        gruInput = inputLayer;
        for step = 1:3
            gruInput = gruNetworks{channel}(gruInput);
        end
        gruInput = reshape(gruInput, [], timeSteps(channel));
        gruInput = layertimeredistribution(gruInput);
        channelOutputs{channel} = gruInput;
    end
    
    combinedOutput = layeradd(channelOutputs{1}, channelOutputs{2}, channelOutputs{3});
    
    fcLayer = layerfullyconnected(50);
    outputLayer = layerregression(1);
    
    layers = [inputLayer, combinedOutput, fcLayer, outputLayer];
    
    net = sequencetosequenceRegressionNetwork(layers);
    
    options = trainingOptions('adam', 'MaxEpochs', 100, 'MiniBatchSize', 32, 'Plots', 'training-progress');
    net = trainNetwork(trainExplanatoryVariables, trainSoilTemperature, net, options);
    
    predictedTemperature = predict(net, testExplanatoryVariables);
end

% 基于四元组损失函数的土壤温度预测模型
function predictedTemperature = quadrupleLossModel(explanatoryVariables)
    inputLayer = layerinput(size(explanatoryVariables, 2));
    hiddenLayer1 = layerfullyconnected(100);
    reluLayer = layerrelu();
    hiddenLayer2 = layerfullyconnected(50);
    outputLayer = layerregression(1);
    
    layers = [inputLayer, hiddenLayer1, reluLayer, hiddenLayer2, outputLayer];
    
    net = multilayerNetwork(layers);
    
    k = 4;
    [clusters, centroids] = kmeans(soilTemperature, k);
    
    function loss = quadrupleLossFunction(predicted, target)
        margin = 1.5;
        numSamples = size(predicted, 1);
        loss = 0;
        for i = 1:numSamples
            sameClusterIndices = find(clusters == clusters(i));
            differentClusterIndices = find(clusters ~= clusters(i));
            for j = 1:numSamples
                if j ~= i
                    if ismember(j, sameClusterIndices)
                        distance = norm(predicted(i) - predicted(j));
                        loss = loss + max(0, margin - distance);
                    elseif ismember(j, differentClusterIndices)
                        distance = norm(predicted(i) - predicted(j));
                        loss = loss + max(0, distance - margin);
                    end
                end
            end
        end
        loss = loss / numSamples;
    end
    
    options = trainingOptions('adam', 'MaxEpochs', 100, 'MiniBatchSize', 32, 'LossFunction', @quadrupleLossFunction);
    net = trainNetwork(trainExplanatoryVariables, trainSoilTemperature, net, options);
    
    predictedTemperature = predict(net, testExplanatoryVariables);
end

% 基于编码器 - 解码器长短期记忆网络的土壤湿度预测模型
function predictedMoisture = encoderDecoderLSTMModel(explanatoryVariables)
    encoderInputSize = size(explanatoryVariables, 2);
    encoderHiddenSize = 100;
    encoderLSTM = layergru(encoderHiddenSize);
    encoderOutput = encoderLSTM(explanatoryVariables);
    
    decoderInputSize = encoderHiddenSize;
    decoderHiddenSize = 50;
    decoderLSTM = layergru(decoderHiddenSize);
    decoderOutput = decoderLSTM(encoderOutput);
    
    combinedOutput = layeradd(decoderOutput, explanatoryVariables);
    
    fcLayer = layerfullyconnected(25);
    outputLayer = layerregression(1);
    
    layers = [explanatoryVariables, encoderOutput, decoderOutput, combinedOutput, fcLayer, outputLayer];
    
    net = multilayerNetwork(layers);
    
    options = trainingOptions('adam', 'MaxEpochs', 100, 'MiniBatchSize', 32);
    net = trainNetwork(trainExplanatoryVariables, trainSoilMoisture, net, options);
    
    predictedMoisture = predict(net, testExplanatoryVariables);
end

% 融合迁移学习的土壤湿度预测时空模型
function predictedMoisture = transferLearningModel(explanatoryVariables)
    spatialFilterSize = [3, 3, 3];
    numSpatialFilters = 16;
    spatialConvLayer = layerconvolution3d(spatialFilterSize, numSpatialFilters, 'Padding', 'same');
    
    temporalHiddenSize = 100;
    temporalLSTM = layergru(temporalHiddenSize);
    
    inputLayer = layerinput(size(explanatoryVariables, 2));
    
    spatialOutput = spatialConvLayer(inputLayer);
    
    reshapedOutput = reshape(spatialOutput, [], size(spatialOutput, 4));
    
    temporalOutput = temporalLSTM(reshapedOutput);
    
    fcLayer = layerfullyconnected(50);
    outputLayer = layerregression(1);
    
    layers = [inputLayer, spatialOutput, temporalOutput, fcLayer, outputLayer];
    
    net = multilayerNetwork(layers);
    
    era5Data = load('era5_soil_moisture.mat');
    era5SoilMoisture = era5Data.soilMoisture;
    era5ExplanatoryVariables = era5Data.explanatoryVariables;
    
    trainRatioEra5 = 0.7;
    numSamplesEra5 = size(era5SoilMoisture, 1);
    numTrainSamplesEra5 = round(trainRatioEra5 * numSamplesEra5);
    trainIndicesEra5 = 1:numTrainSamplesEra5;
    testIndicesEra5 = numTrainSamplesEra5 + 1:numSamplesEra5;
    
    trainEra5SoilMoisture = era5SoilMoisture(trainIndicesEra5, :);
    trainEra5ExplanatoryVariables = era5ExplanatoryVariables(trainIndicesEra5, :);
    
    testEra5SoilMoisture = era5SoilMoisture(testIndicesEra5, :);
    testEra5ExplanatoryVariables = era5ExplanatoryVariables(testIndicesEra5, :);
    
    optionsPreTrain = trainingOptions('adam', 'MaxEpochs', 50, 'MiniBatchSize', 32);
    net = trainNetwork(trainEra5ExplanatoryVariables, trainEra5SoilMoisture, net, optionsPreTrain);
    
    optionsFineTune = trainingOptions('adam', 'MaxEpochs', 50, 'MiniBatchSize', 32, 'InitialLearnRate', 0.001);
    net = trainNetwork(trainExplanatoryVariables, trainSoilMoisture, net, optionsFineTune);
    
    predictedMoisture = predict(net, testExplanatoryVariables);
end

% 使用多通道门控循环单元模型进行土壤温度预测
predictedTemperatureMultiChannelGRU = multiChannelGRUModel(testExplanatoryVariables);

% 使用四元组损失函数模型进行土壤温度预测
predictedTemperatureQuadrupleLoss = quadrupleLossModel(testExplanatoryVariables);

% 使用编码器 - 解码器长短期记忆网络模型进行土壤湿度预测
predictedMoistureEncoderDecoderLSTM = encoderDecoderLSTMModel(testExplanatoryVariables);

% 使用融合迁移学习的时空模型进行土壤湿度预测
predictedMoistureTransferLearning = transferLearningModel(testExplanatoryVariables);

​​​​​​​

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